Methods and Apparatus For Heating and Self-Heating Of Batteries at Low Temperatures

ABSTRACT

A heating circuit for an energy storage device having internal surface capacitance between inputs storing electric field energy between internal electrodes that are coupled to the inputs, with one of the internal electrodes coupled to one of the inputs having characteristics of a series coupled resistor and inductor to a voltage source. The heating circuit including: a power source couplable to one input, wherein the power source provides positive and negative input currents at the input, the positive input current flows into one of the inputs and the negative input current flows out of one of the inputs; and a controller for controlling the power source to provide alternating current between the positive and the negative input currents at one of the inputs at a frequency sufficient to effectively short the internal surface capacitance of the energy storage device to generate heat and raise a temperature of the electrolyte.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of earlier U.S. ProvisionalApplication No. 63/078,251, filed on Sep. 14, 2020, the entire contentsthereof being incorporated herein by reference.

BACKGROUND 1. Field

The present invention relates generally to energy storage devices, suchas supercapacitors and lithium ion batteries, for fast charging andoperation at high rate at very low temperatures, more particularly tomethods and apparatus for fast charging of energy storage devices, suchas supercapacitors and lithium ion batteries and to supercapacitors andlithium ion batteries that are designed to be charged at high rates aswell as for high discharge rate operation at very low temperatures.Herein, by very low temperature it is meant the temperatures at which anelectrolyte in an interior of such energy storage devices at leasthinders charging, such as at temperatures where the electrolyte becomesnearly solid in super-capacitors, usually around −45 degrees C., but aslow as −54 degrees C. or below.

2. Prior Art

A supercapacitor (SC), sometimes referred to as an ultra-capacitor, andformerly referred to as an electric double-layer capacitor (EDLC) is ahigh-capacity electrochemical capacitor with capacitance values up to10,000 Farads at 1.2 volt that bridge the gap between electrolyticcapacitors and rechargeable batteries (each of which are collectivelyreferred to herein as a “supercapacitor”). Such supercapacitorstypically store 10 to 100 times more energy per unit volume or mass thanelectrolytic capacitors, can accept and deliver charge much faster thanbatteries, and tolerate many more charge and discharge cycles thanrechargeable batteries. They are however around 10 times larger thanconventional batteries for a given charge. The construction andproperties of many different types of supercapacitors are well known inthe art.

In certain applications, such as in munitions, supercapacitors may berequired to be charged as well as discharge at very low temperatures,sometimes as low as −40 to −65 degrees F. or even lower. Similar verylow charging and operating temperatures may also be faced in manycommercial applications, such is in supercapacitors used in vehicles fordirect powering or for regeneration circuits used during braking. Atsuch very low temperatures, the supercapacitor electrolyte becomessolid, thereby hampering or preventing ion transportation within theelectrolyte. As a result, the supercapacitor rate of charge anddischarge is greatly diminished. As a result, the user may be unable tocharge or when the temperature levels are not very low and thesupercapacitor is not provided with enough thermal insulationprotection, must wait a relatively long time to charge thesupercapacitor. It is appreciated by those skilled in the art that thisis the case for all currently available supercapacitors.

Similarly, charging methods and devices for currently availablerechargeable batteries, such as lithium ion batteries, cannot be usedfor charging these batteries at low temperatures. Although applicable toany rechargeable battery having an electrolyte interior, reference belowwill be made to lithium ion batteries by way of example. However, suchlow temperatures with regard to lithium ion batteries can be much higherthan that discussed above with regard to supercapacitors, such as closeto zero degrees C., and still hinder charging, damage the battery andeven cause fire hazard because the components of a lithium ion batteryare highly sensitive to temperature. At low temperature, the “viscous”resistance of the electrolyte to the movement of lithium ions increases.This increase in resistance causes higher losses during charging anddischarging of the lithium ion battery. Low temperature charging passes(relatively high) currents through the components representing thebattery electrical-chemical reactions, and is well known to result inso-called lithium plating, which is essentially irreversible, preventsbattery charging, and permanently damages the battery.

SUMMARY

It is therefore highly desirable to have methods and apparatus for rapidcharging of energy storage devices, such as supercapacitors and lithiumion batteries available for storing electrical energy in militaryproducts such as munitions and in commercial products such as inelectric and hybrid vehicles, in vehicle regeneration circuitry andpower tools, in which the charging rate is critical for achieving therequired system performance.

It is also highly desirable to have energy storage devices, such assupercapacitors and lithium ion batteries, with the capability of beingcharged and discharged at significantly faster rates at theaforementioned very low temperatures.

It is also highly desirable that the energy storage devices, such assupercapacitors and lithium ion batteries, could be readily implementedin almost any of the currently available designs to minimize the amountof changes and modifications that have to be done to currentmanufacturing processes for their production.

A need therefore exists for the development of methods and apparatus forrapid charging and discharging of energy storage devices, such assupercapacitors and lithium ion batteries, of different types anddesigns at very low temperatures of sometimes −65 to −45 degrees F. orsometimes even lower.

There is also a need for methods to design and construct energy storagedevices, such as supercapacitors and lithium ion batteries, which can becharged and discharged significantly faster than is currently possibleat very low temperatures.

Such methods and apparatus for rapid charging and discharging ofcurrently available energy storage devices, such as supercapacitors andlithium ion batteries, of different types and designs at very lowtemperatures of sometimes −65 to −45 degrees F. or sometimes even lowerwill allow munitions and vehicles or other devices to be charged and/ordischarged significantly faster and readied for operation. In commercialapplications, such as vehicles in which supercapacitors and/or lithiumion batteries are used, such methods and apparatus for rapid chargingthe same at very low temperatures of sometimes −65 to −45 degrees F. orsometimes even lower will allow the operation of the vehicles and thelike at such very low temperatures.

Such methods to design and construct energy storage devices, such assupercapacitors and lithium ion batteries, that can be charged anddischarged significantly faster than is possible will allow munitionsand/or vehicles using the same to be charged significantly faster andreadied for operation at very low temperatures of sometimes −65 to −45degrees F. or sometimes even lower.

Herein are described novel methods and apparatus for rapid charging anddischarging of currently available energy storage devices, such assupercapacitors and lithium ion batteries, of various types and designsat very low temperatures of sometimes −65 to −45 degrees F. or sometimeseven lower.

Herein are also described novel methods and apparatus for the design andconstruction of energy storage devices, such as supercapacitors andlithium ion batteries, that are designed with the capability of beingcharged and discharged very rapidly at very low temperatures ofsometimes −65 to −45 degrees F. or sometimes even lower.

In addition, herein are also described methods and apparatus for rapidcharging and/or discharging of the energy storage devices, such assupercapacitors and lithium ion batteries, that are designed with thecapability of being charged and discharged very rapidly at very lowtemperatures of sometimes −65 to −45 degrees F. or sometimes even lower.

Although the novel methods and apparatus are described with regard tovery low temperatures as low as −65, such methods and apparatus areapplicable in all low temperature environments, including slightly below0 degrees C., to provide increased charging and discharging performance.

Accordingly, a method is provided for heating an energy storage devicehaving a core with an electrolyte. The method comprising: providing theenergy storage device having inputs and characteristics of a capacitanceacross the electrolyte and the core and internal surface capacitancebetween the inputs which can store electric field energy betweeninternal electrodes of the energy storage device that are coupled to theinputs; switching between an input voltage and a grounding inputprovided to one of the inputs at a frequency sufficient to effectivelyshort the internal surface capacitance of the energy storage device togenerate heat and raise a temperature of the electrolyte; anddiscontinuing the switching when the temperature of the electrolyte isabove a predetermined temperature that is considered sufficient toincrease a charging efficiency of the energy storage device.

The method can comprise providing the input voltage through a firstswitch and providing the grounding input through a second switch,wherein the switching comprises simultaneously coupling the inputvoltage to the one input through operation of the first switch anddecoupling the grounding input from the one input through operation ofthe second switch during a first time interval and thereafter,simultaneously decoupling the input voltage from the one input throughoperation of the first switch and coupling the grounding input to theone input during a second time interval through operation of the secondswitch, wherein the first interval and the second interval aresubsequently repeated at the frequency sufficient to effectively shortthe internal surface capacitance of the energy storage device. The firstswitch can be a normally closed switch that couples the input voltage tothe one input when a first switching voltage is below a firstpredetermined voltage and/or the second switch can be a normally openswitch that decouples the grounding voltage from the one input when asecond switching voltage is below a second predetermined voltage. Theproviding of the grounding input can comprise coupling the one input toa circuit ground through the second switch and a sink resistor. Themethod can comprise selecting the input voltage and a resistance of thesink resistor such that nearly the same charge of the energy storagedevice occurs during the first time interval as discharge from theenergy storage device occurs during the second time interval.

The predetermined temperature can be a first predetermined temperature,where the method can comprise initiating the switching when thetemperature of the electrolyte is below a second predeterminedtemperature that is considered to at least reduce the chargingefficiency of the energy storage device, wherein the secondpredetermined temperature is a lower temperature than the firstpredetermined temperature.

The method can comprise obtaining at least one of a measurement and anapproximation of the temperature of the electrolyte. The obtaining cancomprise directly measuring the temperature of the electrolyte with atemperature sensor positioned at one or more of the electrolyte and asurface of the energy storage device. The obtaining can comprise:applying an initial charging input to the energy storage device,measuring a rate of charging using the initial charging input, anddetermining a charging rate at the initial charging input, wherein if arate of charging is determined to be less than a predetermined chargingrate, the electrolyte temperature is approximated as being less than thepredetermined temperature.

The method can comprise providing a controller for controlling theswitching and the discontinuing. The method can comprise obtaining bythe controller at least one of a measurement and an approximation of thetemperature of the electrolyte. The obtaining can comprise directlymeasuring the temperature of the electrolyte with a temperature sensorcoupled to the controller and positioned at one or more of theelectrolyte and a surface of the energy storage device. The obtainingcan be performed periodically.

The method can comprise producing the input voltage from an AC sourceprovided through an AC to DC converter.

The method can comprise: obtaining an energy storage type for the energystorage device; and retrieving from a look-up table the predeterminedtemperature that corresponds to the obtained energy storage type,wherein the look-up table correlates different energy storage types withcorresponding predetermined temperatures.

The method can comprise coupling the input voltage to the one input tocharge the energy storage device while the temperature of theelectrolyte is above the predetermined temperature.

The energy storage device can be a lithium ion battery or asupercapacitor.

Also provided is a method for charging an energy storage device having acore with an electrolyte. The method comprising: providing the energystorage device having inputs and characteristics of a capacitance acrossthe electrolyte and the core and internal surface capacitance betweenthe inputs which can store electric field energy between internalelectrodes of the energy storage device that are coupled to the inputs;switching between an input voltage and a grounding input provided to oneof the inputs at a frequency sufficient to effectively short theinternal surface capacitance of the energy storage device to generateheat and raise a temperature of the electrolyte; periodically obtaininga measurement that correlates to the temperature of the electrolyte,wherein the switching is initiated when the measurement indicates thatthe temperature of the electrolyte is below a low temperature thresholdthat is considered to at least reduce the charging efficiency of theenergy storage device, wherein the switching is discontinued when themeasurement indicates that the temperature of the electrolyte is above ahigh temperature threshold that is considered sufficient to increase acharging efficiency of the energy storage device, and wherein the lowtemperature threshold is a lower temperature than the high temperaturethreshold; and providing the input voltage to the one input to chargethe energy storage device while the measurement indicates that thetemperature of the electrolyte is above the high temperature threshold.

The application of high frequency current direct heating battery core,mainly the electrolyte, allows the use of almost all currently availablebattery types as well as super-capacitors at temperatures as low as −60degrees C. and even lower. High frequency current flow through a batterycauses a corresponding high frequency oscillatory motion of the ions inthe electrolyte, which generates heat, thereby increasing theelectrolyte and the battery core temperature. Typically, the appliedcurrent frequency can range from a few hundred Hz to several MHz,depending on the battery type and chemistry. To prevent any damage tothe battery and super-capacitor, the high frequency current that ispassed through the battery and super-capacitor must be symmetric, i.e.,have no or negligible net DC component.

Accordingly, methods and examples of their circuit implementation aredescribed that are used to construct the aforementioned direct batteryand super-capacitor heating devices for low temperatures that pass thedesired high frequency current through the battery or super-capacitorwhile automatically keep the high frequency current symmetric with no ornegligible DC component.

It is also highly desirable to have a simple and highly efficient devicethat can be used to keep batteries and super-capacitors at temperaturesat which they can operate at their peak performance levels while theenvironmental temperature is below such temperatures. For example, invery cold environments, the batteries of a vehicle may be initiallyheated by externally provided power so that it could be charged or thatthe vehicle could become operational. However, when the vehicle beginsto travel, external power is no longer available and the batteries maycool down below their full operational performance levels and evenbecome nearly non-operational. In such conditions, it is highlydesirable to provide a very efficient device that can heat the vehiclebattery as needed from its own power (self-heating) so that it is keptoperational at or close to peak performance levels.

It is also appreciated that vehicles, such as trucks or passenger cars,or tractors, snow removal and snow blower trucks, etc., are routinelyparked for certain amount of time or even overnight outdoors at very lowtemperatures, particularly during the winter time. In such cases,external power sources are usually not available, and if their batteriesare very cold, they may not be able to provide enough power to starttheir engine after several hours or overnight parking. In such cases,the operator has the choice of keeping the engine running while inparking at the cost of wasting a considerable amount of fuel and causingunnecessary environmental pollution or using heating blankets over thebatteries and use the battery power to power the heating blankets. Theformer route is costly as well as an environmentally unsound and isbanned in many states to run the engine idle. The latter solution ishighly inefficient since most of the generated heat is lost to theenvironment and therefore can only be used for a relatively shortperiods of times and definitely not for overnight heating of thebatteries.

It is appreciated that most heavy equipment such as trucks use largelead-acid batteries, which when cooled below −10 deg. C., they can onlyprovide a fraction of their full room temperature power. For thisreason, if such equipment must operate at temperature that may reach −20to −30 deg. C. or lower, they may have to carry more batteries so thatcollectively could provide enough power to start their engine. It is,therefore, highly desirable for such vehicles to be provided with themeans to efficiently and with minimal use of the battery power keep thevehicle batteries above certain temperature at which they could provideenough power to start the vehicle engine after a long periods ofparking, such as overnight parking.

Such battery self-heating methods and apparatus are also highlydesirable to be capable of operating while the vehicle engine is runningso that the battery temperature would not drop below a predeterminedthreshold so that the battery stays at or close to its peak performancelevels.

It is appreciated by those skilled in the art that numerous othersystems can also use such self-heating capability to keep them fullyoperational at low temperatures.

Accordingly, methods and examples of their circuit implementation aredescribed that are used to construct highly efficient and simpleself-heating devices for batteries and super-capacitors.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the apparatus ofthe present invention will become better understood with regard to thefollowing description, appended claims, and accompanying drawings where:

FIG. 1 is a schematic of a simplified supercapacitor shown with a lumpedcore with its equivalent lumped internal resistance and inductanceelements.

FIG. 2 illustrates a schematic of an embodiment of a supercapacitorrapid charging system for charging at very low temperatures and supercapacitor to be charged at very low temperatures.

FIGS. 3-7 illustrate embodiments of flow charts of methods for chargingsupercapacitors at very low temperatures.

FIG. 8 illustrates an embodiment of a supercapacitor to be charged atvery low temperatures.

FIG. 9 illustrates a schematic of a supercapacitor charging unit.

FIG. 10 illustrates a circuit diagram of a 2-30 MHz RF Power Amplifier.

FIG. 11 illustrates an equivalent circuitry of a lithium ion battery.

FIG. 12 illustrates a block diagram of a structure of a method ofcharging/discharging a lithium ion battery at low temperatures.

FIG. 13 illustrates a block diagram of main components of an embodimentof a processor controlled lithium ion battery charging and dischargingunit at low temperatures.

FIG. 14 illustrates a block diagram of an alternative embodiment of aprocessor controlled lithium ion battery charging and discharging unitfor low temperature of FIG. 13 for use only as a lithium ion batterycharging unit for all temperatures including at low temperatures.

FIG. 15 illustrates a block diagram of an alternative embodiment of aprocessor controlled lithium ion battery charging and discharging unitfor low temperature of FIG. 13 and for maintaining the battery coretemperature during charging and discharging processes.

FIG. 16 illustrates a block diagram of an alternative embodiment of aprocessor controlled lithium ion battery charging and discharging unitfor low temperature of FIG. 15 for use only as a Lithium ion batterycharging unit for all temperatures including at low temperatures.

FIG. 17 illustrates a block diagram of another alternative embodiment ofa processor controlled lithium ion battery charging and discharging unitfor low temperature of FIG. 15 for use to keep the core temperature of aLithium ion battery above a prescribed temperature for efficientdischarging at all temperatures including at low temperatures.

FIG. 18 illustrates a block diagram of an alternative embodiment of aprocessor controlled lithium ion battery charging and discharging unitfor low temperature of FIG. 17 for use to keep the core temperature of aLithium ion battery above a prescribed temperature for efficientdischarging at all temperatures including at low temperatures.

FIG. 19 illustrates a block diagram of an alternative embodiment of aprocessor controlled lithium ion battery charging and discharging unitfor low temperature of FIG. 18 for use to keep the core temperature of aLithium ion battery above a prescribed temperature for efficientdischarging at all temperatures including at low temperatures.

FIG. 20 illustrates a flow chart diagram for charging a lithium ionbattery for low temperature by keeping the core temperature of theLithium ion battery above a prescribed temperature for efficientcharging at all temperatures including at low temperatures.

FIG. 21 illustrates a flow chart diagram of discharging a lithium ionbattery for low temperature by keeping the core temperature of theLithium ion battery above a prescribed temperature for efficientdischarging at all temperatures including at low temperatures.

FIG. 22 illustrates a circuit diagram of an embodiment of a heatingcircuit for a battery or energy storage device.

FIG. 23 is a schematic model of a supercapacitor having additionaldetail as compared to the model of FIG. 1.

FIG. 24 illustrates a circuit diagram implementation of the embodimentof the battery heating circuit of FIG. 22.

FIG. 25 illustrates a circuit diagram of the embodiment of the batteryheating circuit of FIG. 22 with a battery temperature sensor andcontroller that activates the battery heating circuit when a prescribedlow temperature threshold is detected.

FIG. 26 illustrates an alternative circuit diagram of the embodiment ofthe battery heating circuit of FIG. 25.

FIG. 27 illustrates the circuit diagram of another embodiment of thebattery heating circuit.

FIG. 28 illustrates a circuit diagram of the embodiment of the batteryheating circuit of FIG. 27 with a battery temperature sensor andcontroller that activates a battery heating circuit when a prescribedlow temperature threshold is detected.

FIG. 29 illustrates a circuit diagram of another embodiment of a batteryheating circuit.

FIG. 30 illustrates a circuit diagram of the embodiment of the batteryheating circuit of FIG. 29 with a battery temperature sensor andcontroller that activates a battery heating circuit when a prescribedlow temperature threshold is detected.

FIG. 31 illustrates a plot of a Li-ion battery heating as a function oftime from a temperature of −30 deg. C. to 20 deg. C. using the heatingcircuit of embodiment of 27.

FIG. 32 illustrates a plot of an internal resistance of a standard 18650cell Li-ion battery (battery part number is LGABB418650) in atemperature range of −55° C. to 45° C.

FIG. 33 illustrates a plot of the internal inductance of a standard18650 cell Li-ion battery (battery part number is LGABB418650) in atemperature range of −55° C. to 45° C.

FIG. 34 illustrates a circuit diagram of another embodiment of a batteryheating circuit.

FIG. 35 illustrates the circuit diagram of the embodiment of FIG. 34 asmodified to provide a sinusoidal high frequency heating AC voltage.

FIG. 36 illustrates a circuit diagram of another embodiment of a batteryheating circuit.

FIG. 37 illustrates a circuit diagram of the embodiment of FIG. 36 asmodified to provide a sinusoidal high frequency heating AC voltage.

FIG. 38 illustrates an alternative modified circuit diagram of theembodiment of FIG. 37.

FIG. 39 illustrates a plot of the available battery current at the ratedvoltage as a function of temperature for several battery types.

FIG. 40 illustrates a circuit diagram of another embodiment of a batteryheating circuit.

FIG. 41 illustrates a modified circuit diagram of the embodiment of thebattery heating circuit FIG. 40.

FIG. 42 illustrates a circuit diagram of another embodiment of a batteryheating circuit.

FIG. 43 illustrates a modified circuit diagram of the embodiment of thebattery heating circuit FIG. 42.

FIG. 44 illustrates the block diagram of another embodiment of a batteryheating device.

FIG. 45 illustrates the operation of the “heating engine” in the blockdiagram of the embodiment of FIG. 44 of a battery heating device.

FIG. 46 illustrates typical switching waveforms and the battery currentwaveform that are used in the embodiment of FIG. 44 of a battery heatingdevice.

FIG. 47 illustrates one possible implementation of the hardware shutdowncircuit for the embodiment of FIG. 44 of a battery heating device.

FIG. 48 illustrates an example of a current waveform during one heatingcycle of for the embodiment of FIG. 44 of a battery heating device.

FIG. 49 illustrates the actual measured current response during theheating of a 12 V Type 31 lead-acid battery commonly used in trucks.

FIG. 50 illustrates the basic circuit diagram of the first highefficiency self-heating device embodiment of the present invention.

FIG. 51 illustrates the block diagram of the first high efficiencyself-heating device embodiment of the present invention.

FIG. 52 illustrates a circuit diagram for the first high efficiencyself-heating device embodiment of the present invention of FIG. 50.

FIG. 53 illustrates the plots of an example of the battery andenvironmental temperatures during self-heating of a battery with theself-heating device embodiment of FIG. 52.

FIG. 54 illustrates the circuit diagram of the high efficiencyself-heating device embodiment of FIG. 52 with the added heatingresistor to increase the overall heating efficiency of the self-heatingsystem.

FIG. 55 illustrates a circuit diagram for another high efficiencyself-heating device embodiment of the present invention.

FIG. 56 illustrates plots of typical current and voltage waveforms inthe in series resonant circuit of the self-heating circuit of FIG. 55during one cycle of self-heating.

FIG. 57 illustrates circuit diagram for a higher efficiency self-heatingdevice embodiment of the present invention resulting from modificationof the embodiment of FIG. 55 and its process of operation.

FIG. 58 illustrates plots of typical current and voltage waveforms inthe resonant circuit of the self-heating circuit of FIG. 57.

FIG. 59 illustrates plots of typical current and voltage waveforms inthe resonant circuit of the self-heating circuit of FIG. 57 from thestored energy in the circuit capacitor.

FIG. 60 illustrates plots of typical current and voltage waveforms inthe resonant circuit of the self-heating circuit of FIG. 57 for its fullcycle of high efficiency battery heating.

FIG. 61 illustrates the operational flow chart for the self-heatingembodiments of FIGS. 55 and 57 with automatic circuit parameteradjustment capability.

DETAILED DESCRIPTION

All currently available supercapacitor types and designs exhibitinternal resistance and inductance, which can be modeled as being inseries. Both internal resistance and inductance of supercapacitors arerelatively low. The inductance of supercapacitors is significantlyhigher for wound supercapacitors as compared to those that are flat andstacked in construction. The leakage current may be represented by aseparate resistor in parallel with the capacitor. In general, thesupercapacitor resistance may be ignored in short term operations. Thesupercapacitor inductance can also be ignored for low frequencyoperations.

In the schematic of FIG. 1, a simplified model of a supercapacitor 20 isshown with a lumped capacitor core 21 within which the aforementionedequivalent internal resistance and inductance are shown as two pairs ofin-series resistors and inductors, which are connected to thesupercapacitor capacitance C. In FIG. 1, the in-series resistor andinductor pairs are indicated by the resistances R1 and R2 andinductances L1 and L2. In most supercapacitors, the resistances of theresistors R1 and R2 are very low. In the present model, the pairs oflumped in-series resistors and inductors are connected on one end to thesupercapacitor capacitance C and on the other end to the supercapacitorterminals 22. In FIG. 1, the internal resistance of the supercapacitor,which is the cause of leakage is modeled as a lumped resistor R3. InFIG. 1 and for the sake of simplicity and since the simplification doesnot affect the methods and apparatus for charging and dischargingsupercapacitors to be described, the electrical model of thesupercapacitor is considered to be as shown in FIG. 1.

In the first embodiment shown schematically in FIGS. 2, 3 and 5, asupercapacitor charger unit 11 having an internal processor 11 a wouldfirst obtain the internal temperature of the supercapacitor core at stepS1 a or S1 b. Such processor comprises a hardware, component such as aPLC or CPU and can include software and a memory storing such softwareand also storing data such as predetermined values used in the methodsdescribed below. In applications, such as munitions in which themunitions has been stored at the ambient temperature, the supercapacitorcore temperature may be obtained by measuring the ambient temperature atstep S1 a and approximating the internal temperature of thesupercapacitor core using some function of the ambient temperature, suchas equating the ambient temperature to the supercapacitor coretemperature. Alternatively, the supercapacitor core temperature can bedirectly measured by an internal sensor 12 (such as a thermocouple basedsensor or other temperature measurement sensors known in the art), withthe measured temperature signal being provided to the processor 11 a viawiring 13 connected to the sensor capacitor terminals 14. The sensor 12is used by the processor 11 a to determine if the supercapacitor can becharged at its regular rate or if the core temperature is so low thatthe supercapacitor electrolyte has become solid or very close to it,thereby hampering or preventing ion transportation within theelectrolyte and preventing the supercapacitor from being rapidly chargedat its regular (liquid electrolyte state) rate. As yet anotheralternative, the temperature sensor can be positioned on an exteriorsurface of the supercapacitor and the obtained temperature used toapproximate the internal temperature of the supercapacitor core usingsome function of the exterior surface temperature, such as equating theexterior surface temperature to the supercapacitor core temperature.

Alternatively, as shown in FIG. 5, the supercapacitor core temperaturemay be obtained based on an assumption, such as by applying the regularcharging voltage (or any appropriate initial voltage level) to the supercapacitor via the charging unit 11 at step S1 b and if the processor 11a determines that the supercapacitor does not charge at its regular rateat step S2 b, i.e., for example, the measured charging current issignificantly lower than a known regular charging current rate, then theprocessor 11 a can assume that the supercapacitor core temperature isvery low and below that where the same can be charged at its regular(liquid electrolyte state) rate.

Hereinafter, as discussed above, very low temperature is used toindicate temperature levels at which the supercapacitor electrolyte isrendered solid or effectively incapable of allowing relatively freetransport of its ions.

It will be appreciated by those skilled in the art that for safetyreasons, the processor 11 a of the charger unit 11 can also determinethe charge level of the supercapacitor prior to the start of thecharging cycle. In addition, the temperature sensor 12 can be employedto ensure that a low charging rate is in fact due to low supercapacitorcore electrolyte temperature level as was earlier described.

In the schematic of FIG. 2, the charger unit 11 is shown to be poweredinternally, such as by a battery. In many applications, however, thecharger unit 11 can be powered by an external source (not shown). Thecharging unit 11 functions similarly irrespective of the source ofcharger unit 11 power.

Then, once the processor 11 a has determined that the supercapacitorcore temperature is very low and that due to the very low temperaturelevel the supercapacitor (which can also be determined not to be fullycharged) cannot be rapidly charged at either step S2 a or S2 b, thecharger unit 11 can begin to charge the supercapacitor at step S5 a. Inthe schematic of FIG. 2 the charger unit 11 is shown to be connected tothe supercapacitor 20 via wires 15 connecting the terminals 22 of thesupercapacitor 20 to the corresponding terminals 16 of the charger unit11.

However, if the processor 11 a determines the core temperature of thesuper capacitor is not less than a predetermined temperature (e.g., thecore is at a temperature above which normal charging can be conducted)at step S2 a or S2 b (the determination at step S2 a or S2 b is NO), thecharger unit would charge the supercapacitor conventionally at step S3,and continue to do so until the super capacitor is determined to befully charged at step S4 or charging is otherwise terminated.

On the other hand, if the determination at step S2 a or S2 b is YES, thecharger unit 11 can input one or more of a predetermined voltage andcurrent to the terminals 22 of the supercapacitor which will causeinternal components of the energy storage device to generate heat. As afirst exemplary input, the charger unit 11 can apply a relative highfrequency voltage to the supercapacitor at step S5 a. The high frequencyvoltage can be at a peak voltage of around the maximum allowablecharging supercapacitor voltage or even significantly higher. Here, highfrequency means a frequency at which the supercapacitor capacitoreffectively shorts and inductances L1 and L2 and resistances R1 and R2are caused to generate heat. The processor 11 a can then periodicallycontinue to obtain the supercapacitor core temperature by any of themethods discussed above, such as at some predetermined intervals (shownby line S6 in FIGS. 3 and 5). The periodic obtainment of thesupercapacitor core temperature can be by direct measurement orassumption as discussed above, such as by measuring the internaltemperature with the temperature sensor 12 at step S1 a or by attemptingto charge the capacitor at the regular charging voltage at step S1 b andmeasuring the charging rate from the charging current. Alternatively,more than one method can be used, such as both methods (S1 a and S1 b)for measuring the core temperature until either the core (thesupercapacitor electrolyte) temperature has reached a desired level forproper charging of the supercapacitor or until the supercapacitornominal charging rate has been reached. At which time the applied highfrequency voltage signal is terminated at step S2 a and/or S2 b and theprocessor 11 a instructs the charging unit 11 to conventionally chargethe supercapacitor to the desired level at steps S3 and S4. Thetemperature level and/or charging rate measurements may be repeated asneeded, such as at regular intervals, particularly at very low ambienttemperature conditions to ensure that the process of charging is notinterrupted by “re-freezing” of the supercapacitor electrolyte.

An alternative embodiment is now described using the schematic of FIG. 2and the flow diagrams of FIGS. 4 and 6 in which similar steps arenumbered similarly to those illustrated in FIGS. 3 and 5, respectively.In the alternative embodiment, once the core 12 of the (not fullycharged) supercapacitor 20 is determined to be at very low temperatureat step S2 a or S2 b using any one or combinations of aforementionedtechniques, the processor 11 a instructs the charging unit 11 to heatthe core 12 at step S5 b by passing a constant current through theequivalent internal resistance R3 through the supercapacitor terminals22 and the aforementioned two pairs of serially connected resistors andinductors. The current is generated by the charging unit 11 through thewiring 15. In general, and depending on the type and design of thesupercapacitor 20 and its charging state and the electrolytetemperature, the current may be applied at voltages that aresignificantly higher than the voltage rating of the supercapacitor. Thisis usually possible since frozen electrolytes of a capacitor with lowlevel of charge can withstand significantly higher voltages. When usingthe heating voltages that are above the rated voltage of thesupercapacitor, the processor 11 a can regularly monitor the coretemperature and the charging state of the supercapacitor at S6 andproperly lower the heating voltage as the supercapacitor begins to becharged at or close to its nominal rate.

In general, due to the very high internal resistance level R3 of mostsupercapacitors, the methods illustrated in FIGS. 3 and 5 of providingheat to the supercapacitor core via the equivalent inductances L1 and L2of the supercapacitor may be more effective. Such methods illustrated inFIGS. 3 and 5 may also be safer since the high frequency current may beapplied at or even above the rated voltage of the supercapacitor.However, it will be appreciated by those skilled in the art that sincethe inductor core in this case is in effect the conductivesupercapacitor electrolyte, the amount of heat that may be generated inmany supercapacitors could be relatively low.

In the lump model shown in FIG. 1, the aforementioned heat generated persecond (P) by the application of a constant voltage to thesupercapacitor terminals is given by

$\begin{matrix}{P = \frac{V^{2}}{R_{1} + R_{2} + R_{3}}} & (1)\end{matrix}$

As can be seen from the above equation, since the leakage resistance R3is very large, the amount of heat that can be generated per second for arelatively low voltage that can be applied to a supercapacitor (with,for example, a rate voltage of 2.7 Volts) is very small. For example,for a typical 100 F supercapacitor with a rated voltage of 2.7 V andwith a serial resistance R1+R2=50 mΩ, and leaking resistance R3=10 kΩ,will, according to equation (1) above only generate heat at a rate of:

$P = {\frac{\left( {{2.7}V} \right)^{2}}{\left( {{10\mspace{14mu} k\;\Omega} + {50\mspace{14mu} m\;\Omega}} \right)} = {{0.7}3\mspace{14mu}{mW}}}$

In another alternative embodiment, the following method can be usedinstead of the previously described application of a constant voltage tosignificantly increase the above rate of heat generation within the core21 of a typical supercapacitor 20, such as the one shown schematicallyin FIG. 1. In this method, shown in FIG. 7, once the charger unit 11 hasdetermined that the battery is not charged completely and that thebattery core is at a very low temperature at steps S1 c and S2 c, as waspreviously described, then the charger unit 11 would apply analternating current (AC) with a peak voltage of V_(p) at a highfrequency f to the terminals at step S5 c. The behavior of the lumpedcircuitry (consisting of the resistors R1, R2 and R3 and inductors L1and L2 as shown in FIGS. 1 and 2) will now be very different than thatindicated by the above equation (1). At a high frequency f, thecapacitor C provides very low impedance, effectively shorting theleakage resistor R3 which is in parallel with it. As a result, the totalresistance to the applied current becomes very small since theresistances R1 and R2 are very small. As a result, the total heatgenerated per second becomes very large and therefore the very coldsupercapacitor core electrolyte can be heated very rapidly to thetemperature at which it can be charged at or close to its nominalcharging rate. It is noted that at such very high frequencies, theinductors L1 and L2 also provide high impedance but would usuallycontribute significantly less heat in a supercapacitor environment thanthose generated by low resistances R1 and R2. The heat generated persecond (power P) is given approximately by the equation (2) below.

$\begin{matrix}{P = {\frac{1}{2}\frac{V_{p}^{2}}{R_{1} + R_{2} + {2\pi\;{f\left( {L_{1} + L_{2}} \right)}} + \frac{R_{3}}{1 + {2\pi\;{fCR}_{3}}}}}} & (2)\end{matrix}$

For the aforementioned 100 F supercapacitor with a typical totalinductance of L1+L2=0.06 pH and R1+R2=50 mΩ, and leaking resistanceR3=10Ω, with an applied AC voltage of V_(p)=1 V at frequency f=1,000 Hz,the heat generated per second can reach 9.3 W. It is noted the abovecalculations are approximate and does not consider change in thesupercapacitor capacitance at very low temperatures and with the appliedhigh frequency voltage.

It will be appreciated by those skilled in the art that the charger unit11 would require not only the processor 11 a but any electronics andlogic circuitry for the core temperature measurement and for providingthe indicated currents and voltage inputs for the describedsupercapacitor heating process as well as safe charging of thesupercapacitor. These technologies are widely used in practice and areconsidered to be well known in the art.

In the above embodiments, the inductance or the internal resistance ofthe supercapacitors is used by the described charging unit to heat upthe supercapacitor core (mainly its electrolyte) to a temperature atwhich electrolyte ions are provided with enough mobility to allow rapidcharging of the supercapacitor. It consists of a series resistance andan inductance, and the leakage current is represented by a resistor inparallel with the capacitor, FIG. 1. The series resistance (R1 and R2 inFIG. 1) ranges from a few milliohms to several tens milliohms. Theinductance (L1 and L2 in FIG. 1) depends on the construction and can beignored for low frequency operation. The leakage resistance can also beignored for short-term operation. The electrolyte in supercapacitorsforms a conductive connection between the two electrodes whichdistinguishes them from electrolytic capacitors where the electrolyte isthe second electrode (the cathode). Supercapacitor electrodes aregenerally thin coatings applied and electrically connected to aconductive, metallic current collector. Electrodes must have goodconductivity, high temperature stability, long-term chemical stability,high corrosion resistance and high surface areas per unit volume andmass. Other requirements include environmental friendliness and lowcost.

Referring now to FIG. 8, no matter the type and design of thesuper-conductor and its electrodes, another embodiment relates toadditional resistive and/or inductive elements added to thesupercapacitor electrode surface or otherwise distributing suchresistive and/or inductive elements throughout the supercapacitor core.Similarly, such additional resistive and/or inductive elements can alsobe added to a rechargeable battery, such as a lithium ion battery. Theseadded resistive and/or inductive elements can be electrically insulatedby dielectric materials to prevent them from interfering with theoperation of the energy storage device. The added resistive R4 and/orinductive elements L3 can be distributed throughout the core and asclose as possible to its electrolyte material. Then when the coretemperature is determined to be low as was previously described, passingcurrent through the added resistances generates heat to increase thetemperature of the electrolyte and thereby allowing charging at itsnominal rate once the core temperature rises above some predeterminedtemperature or charging ability. When an inductive element is added, analternating current of high enough frequency can be used for the heatingof the electrolyte thereby facilitating the process of rapid charging atvery low temperatures. With such a supercapacitor 20 a, additionalterminals 14 a can be provided for inputting the required electricalinput for heating the core though independent wiring 13 a from thecharger unit of electronic logic can be provided to use only one set ofterminals 22 to both charge the supercapacitor 20 a and input theadditional inductor(s) L3 and resistor(s) R4 for heating the core.

A block diagram of a supercapacitor testing unit 100 is shown in FIG. 9.A function generator 102 is provided, such as a 25 MHz arbitrarywaveform generator. A power amplifier 104 is also provided and can beconstructed by modifying an available 2-30 MHz RF power amplifier bymatching the supercapacitor impedance and the required power range asdescribed below. The DC power source 106 is provided by a regulatedsource with output voltage and current limit setting. The test load oruser device 108 can be a high power resistor, which is used to measurethe available energy stored in the supercapacitor.

The function generator frequency and the power amplifier voltageamplitude can be manually set. A host computer 110 equipped with a DAQand DSP board can provide the means of controlling the process and fordata collection and online analysis and feedback. A DSP board clock canbe used to provide for fast input/output operations and sampling time.The provided system can allow continuous measurement of the voltage andcurrent across the load and the consumed power, thereby the loadimpedance. The DC power source 106 can also be controllable by the DSPbased controller 110 to achieve a desired charging profile. The testload can be used to measure an amount of energy the chargedsupercapacitor can provide following charging. A switch 112, controlledby the DSP controller 110, can be used to connect the supercapacitor 114to the desired circuitries. A set of voltage and current sensors 116,118 report their values to the DSP A/D converter via the DAQ. Thecontroller 110 can communicate with a host computer to exchange thecommand and status of each device. The DSP controller 110 can alsogenerate charging pulses.

The supercapacitor testing unit can be designed to apply a highfrequency sinusoidal AC voltage signal with and without DC bias to thesupercapacitor load. The voltage and frequency of the AC signal can bemanually or automatically controlled. The voltage across the load andthe current passing through the supercapacitor load and their phase aremeasured. The power applied to the load and the impedance of the loadcan then be calculated.

The high frequency 25 MHz function generator 102 can be used as an inputto the power amplifier 104. The power amplifier 104 can be constructedby the modification of the input and output impedance of an existing RFpower amplifier. A circuit diagram of an existing 2-30 MHz RF poweramplifier design is shown in FIG. 10. The nominal power output of thisdevice can be 30 Watt, which is appropriate for superconductor charging.

An existing host computer will be provided with a DAQ and a DSP boardfor this purpose. The required software for running the system withproper data communication, sensor data acquisition and processing andgenerating the required control signals can be stored in a memory (notshown) accessible by the controller 110.

The charging unit 100 can measure the impedance of the supercapacitor114 at different AC frequency, temperature and voltage. The functiongenerator 102 can be used to generate sinusoid with adjustable voltagesignal, for example up to 25 MHz. The power amplifier 104 will thenproduce and apply an AC voltage at a predetermined (preset) voltagelevel to the supercapacitor. The switch 112 controlled by the pulsegenerator will be used to apply the AC voltage to the supercapacitor 114for a predetermined time period, such as an adjustable short duration of10 to 100 microseconds depending on the AC voltage frequency. The shortduration of the input power ensures that the total input energy isnegligible. The input voltage and current waveform is then measured andused to calculate the supercapacitor impedance.

Tests of the superconductor charging can be conducted at varioustemperatures, such as at −20° C., −25° C., −35° C., −45° C., −48° C.,−54° C., and −65° C. The tests can also use various AC voltageamplitudes, such as 2.7 V, 3.2 V, 4.5 V, 6 V, 8 V and 10 V. The ACvoltage frequency range can be 2 MHz to 25 MHz, and testing can beperformed in 0.5 MHz steps.

As was previously described, the application of high frequency ACvoltage to the supercapacitor is for the purpose of heating thesupercapacitor core at low temperatures, in particular its electrolyte,before charging it with an applied DC voltage.

An objective of the testing device is to determine at what point the ACvoltage must cease and the DC charging should begin so as to build adatabase for use in the methods described above. At very lowtemperatures of below around −45° C. to 48° C., the electrolyte isnearly frozen solid and the impedance of the supercapacitor is veryhigh. But as the electrolyte becomes active (melt), the rapid increasein the effective capacitance of the supercapacitor causes the impedanceto rapidly drop, thereby causing the passing current level to increaseaccordingly. In the tests, the AC current level is measured and after ithas increased by a factor of 10, 25, 50, 75 and 100 then the AC voltagecan be switched off and the DC charging voltage applied to thesupercapacitor. In the test, for example, the supercapacitor can becharged at 3.2 V until the charging current drops to 20 mA, at whichpoint the supercapacitor will be considered to be fully charged. Theavailable stored energy is then measured by discharging the storedenergy in the supercapacitor through the test load 108.

The AC current and voltage profiles and the DC charging time arerecorded. The tests can be performed while the supercapacitor is insidea temperature chamber 120. The tests can be performed with the capacitorwrapped in a typical thermal insulation jacket and without thermalinsulation to mimic a supercapacitor installed within a housing thatprovides certain level of thermal insulation against heat loss andoutside of any housing, respectively.

During the tests, the supercapacitor 114 will be considered damaged ifthe stored energy is less than 95% of the expected available storedenergy.

Such testing can be used to optimize the above described methods forcharging supercapacitors at low temperature to achieve full charge inminimum amount of time and used to formulate a general time optimalstrategy for charging supercapacitors at low temperatures. A range of ACvoltage and frequency for preheating of the supercapacitor and itsfollow up DC charging and the expected optimal AC to DC switching pointcan be determined for different low temperature levels which can betested and fine-tuned to obtain the desired time-optimal strategy forimplementation.

Thus, the above testing device and methods can be used to obtainstatistical information regarding the time needed to charge various sizeand configuration supercapacitors to full charge at various lowtemperatures. The statistical information generated can include the meantime required to charge a capacitor at a given temperature and itsstandard deviation at a certain confidence level, such as 95%.

It will be appreciated by those skilled in the art that the disclosedtesting device and method for charging supercapacitors at lowtemperatures can be applied to the other methods described above (suchas at FIGS. 3-6) and/or for different types of commonly knownsupercapacitors, ultracapacitors and so-called hybrid capacitors and thelike as well as to rechargeable batteries, such as lithium ionbatteries.

The above method and devices for rapid charging of supercapacitors atlow temperatures can also be used to similarly enable and/orsignificantly increase the charging rate of lithium-ion and othersimilar rechargeable batteries at low temperatures. As discussed above,low temperature charging is in general even more an issue forlithium-ion and other similar rechargeable batteries since their rate ofcharging is low at even higher temperatures than supercapacitors,usually even a few degrees below zero C.

In the case of lithium-ion and other similar rechargeable batteries,similar to the previously described method for supercapacitors, thecharging process includes similar steps. After determining that thelithium ion battery requires charging and that its core is at a lowtemperature that prohibits/minimizes charging, the battery electrolyteand electrodes are heated by similar methods as described above withregard to FIGS. 3-7, by inputting one or more of a predetermined voltageand current input to terminals of the battery causing internalcomponents thereof to generate heat, such as with the application of anAC high frequency voltage, usually in the order of 1-10 MHz andsometimes higher depending on the battery size and construction. Thenonce the battery core, particularly its electrolyte, has reached adesired predetermined temperature or charging ability, which may bedetected directly with a temperature sensor as described above orassumed, such as by detecting the charging rates with AC and/or DCvoltages, as also described above, the battery can be chargedconventionally using DC voltages following well known electronic andlogic circuitry and procedures to ensure safe and rapid charging.

It will be appreciated by those in the art that in many cases inlithium-ion and other similar rechargeable battery charging (includingsupercapacitor charging), the optimal charging time can be achieved byoverlapping AC voltage and DC voltage charging during a portion of thetime, usually before switching from the AC to DC voltages.

A basic operation of Lithium ion batteries may be approximately modeledwith the equivalent (lumped) circuitry shown in FIG. 11. In this model,the resistor R_(e) is considered to be the electrical resistance againstelectrons from freely moving in conductive materials with which theelectrodes and wiring are fabricated. The equivalent resistor R_(I)represents the (“essentially viscous”) resistance to free movement oflithium ions by the battery electrolyte. The equivalent inductor L_(I)represents the (“essentially inertial”) resistance to change in itsstate of motion, which is insignificant until the frequency of therequired motion becomes extremely high. The capacitor C_(s) is thesurface capacitance, which can store electric field energy betweenelectrodes, acting similar to parallel plates of capacitors. Theresistor R_(c) and capacitor C_(c) represent the electrical-chemicalmechanism of the battery in which C_(c) is intended to indicate theelectrical energy that is stored as chemical energy during the batterycharging and that can be discharged back as electrical energy during thebattery discharging, and R_(c) indicates the equivalent resistor inwhich part of the discharging electrical energy is consumed (lost) andessentially converted to heat. The terminals A and B are intended toindicate the terminals of the lithium ion battery and C and D are otherinternal points in the circuitry.

It will be appreciated by those skilled in the art that many differentLithium ion types and designs and different chemical compositions arecurrently available. It is also appreciated by those skilled in the artthat other models of the Lithium ion batteries have also been developed.The model presented in the schematic of FIG. 11 does however representthe basic components of Lithium ion batteries as far as the disclosedmethod and apparatus for charging such batteries at low temperatures areconcerned. Therefore the methods and apparatus described herein appliesto all different types and designs of Lithium ion batteries with alldifferent design structures and chemistries and not just those havingthe configuration represented by FIG. 11. The reasons that currentlyavailable Lithium ion battery charging methods and devices cannot beused for charging these batteries at low temperatures of even close tozero degrees C. are briefly described above and well described in thepublished literature and have been shown to damage the battery and evencause a fire hazard if used.

In the approximated equivalent (lumped) circuitry model of Lithium ionbatteries shown in FIG. 11, three components of the battery, namelyR_(I), R_(c) and C_(c), are highly sensitive to temperature. At lowtemperature, the resistance of the resistor R_(I) increases due to theincrease in the “viscous” resistance of the electrolyte to the movementof lithium ions. This increase in resistance causes higher losses duringcharging and discharging of the lithium ion battery. Low temperaturecharging passes (relatively high) currents through the indicatedcomponents R, and C, representing the battery electrical-chemicalreactions, and is well known that results in so-called lithium plating,which is essentially irreversible, prevents battery charging, andpermanently damages the battery.

An embodiment of a method for charging lithium ion batteries at lowtemperatures can be described as follows. Consider the circuit model ofFIG. 11. If an AC current with high enough frequency is applied to thebattery, due to the low impedance of the capacitor C_(s), there will beno significant voltage drop across the capacitor, i.e., between thejunctions C and D, and the circuit effectively behaves as if thecapacitor C_(s) were shorted. As a result, the applied high frequency ACcurrent is essentially passed through the resistors R_(e) and R_(I) andnot through the R_(c) and C_(c) branch to damage the electrical-chemicalcomponents of the battery. Any residual current passing through theR_(c) and C_(c) branch would also not damage the battery due to a highfrequency and zero DC component of the applied current. The highfrequency AC current passing through the resistors R_(e) and R_(I) willthen heat the battery core, thereby increasing its temperature. If thehigh frequency AC current is applied for a long enough period of time,the battery core temperature will rise enough to make it safe to chargeusing commonly used DC charging methods.

Furthermore, when the demanded frequency of AC current becomes high, theinductance L_(I) indicates high AC voltage potential requirement fromthe charging device. In other words, while there is an AC voltagelimitation on the charging device, the inductance L_(I) would becomedominate when the frequency is high enough so that all voltage potentialdrop falls across it. Even though there is still part of the energybeing transferred into heat from this inductor, it is far less than fromR_(I) Therefore, the high frequency AC current can be chosen with theinductance L_(I) taken into consideration.

In the device designed to provide the aforementioned high frequency ACcurrent to raise the battery core temperature to a safe chargingtemperature, provision can be made to periodically assess thetemperature status of the battery core and determine if a safe chargingtemperature level has been reached.

Although temperature sensors can be used, similarly to that discussedabove with regard to the supercapacitor of FIG. 12, in the method andapparatus for charging Lithium ion batteries at low temperatures, twobasic methods may be used to assess the battery core temperature withoutthe need for temperature sensors (thus, not requiring a specialconfiguration of the lithium ion battery for use in such methods or withsuch apparatus). In one method, as the aforementioned high frequency ACcurrent is applied to the battery, the battery impedance is regularlymeasured. Since the resistance of the resistor R_(I) is high at lowtemperatures, the level of battery impedance indicates if the batterycore temperature is low or around a safe temperature for charging. Whenusing this method, the impedance of the battery can be measured a priorifor the charger to use to determine when the battery core safe chargingtemperature has been reached.

A second method for determining if the battery core temperature hasreached a safe charging temperature level while applying theaforementioned high frequency AC current is as follows. In this method,the high frequency AC current is periodically turned off and current isdischarged from the battery through a resistive load for a very shortduration. If the battery core is still cold, then the voltage across theload will be low.

It will be appreciated by those skilled in the art that both methodsdescribed above can be readily incorporated in the battery chargingunit. In fact, the electrical and electronic circuitry required to applythe aforementioned high frequency AC current as well the above oneand/or both methods of assessing the Lithium ion battery coretemperature for safe charging may be readily incorporated in one singlecharging unit. Such a unit can also use commonly used methods to chargethe battery once the battery core temperature has been raised to a safecharging level.

Furthermore, once DC charging has begun, the charging unit may beprogrammed to periodically assess the battery core temperature and ifdetects that the temperature is approaching an unsafe (low) temperature,then the high frequency AC current would be turned on and the DCcharging current is turned off. Alternatively, a high frequency ACcurrent may be superimposed on the charging DC current.

The Lithium ion battery may also be provided with a temperature sensorto measure its temperature such as those used in some currentlyavailable Lithium ion batteries. The temperature sensor input, which canbe in addition to one or both aforementioned methods, may then be usedto determine the safe charging temperature of the battery.

The aforementioned high frequency AC current may also be used toincrease Lithium ion battery core temperature at low temperatures toachieve higher discharge rates. As such, the present method provides themeans of charging Lithium ion batteries at low temperatures as well asproviding the means of increasing the performance of Lithium ionbatteries, i.e., increasing their discharge rate, at low temperatures.

The block diagram of the apparatus using the present novel method forcharging and/or discharging Lithium ion batteries 206 having anelectrolyte battery core 208 at low temperature is shown in FIG. 12. Thecharging/discharging unit 200 (collectively referred to herein as a“charging unit”) is provided with electrical and electronic circuitry toprovide the aforementioned high frequency AC current and the charging DCcurrent, both with voltage controls, and can include a processor 202,such as a microprocessor or CPU for controlling the process of measuringthe battery core temperature as previously described and increasing thecore temperature if below the battery safe charging temperature andcharging when the battery core temperature above the said safe chargingtemperature. The charging unit 200 having wiring to connect to theterminals 210 of the battery 206. The process steps for carrying outsuch methods can be stored as software on a memory device accessible bythe processor 202. The charging unit 200 would periodically check thetemperature by using one or both aforementioned methods based on thebattery impedance and/or alternatively from an external or internalbattery temperature sensor source 204 to properly direct the chargingprocess.

Alternatively, the charging unit of FIG. 12 may function as a chargingand discharging control unit and increase the battery core temperaturewhen it is below the aforementioned safe charging temperature forcharging by applying an appropriate high frequency AC current to thebattery to be followed by a DC charging current. And if the batterytemperature is low enough to significantly degrade its performance,i.e., its desired discharge rate, the charging unit 200 would also applythe high frequency AC current to the battery 206 to increase its coretemperature to increase its discharge rate.

An embodiment 300 of the Lithium ion charging and discharging unit isshown in the block diagram of FIG. 13. Although the unit 300 can be usedto solely charge lithium ion batteries at low temperatures, the unit 300is intended for use as a charging and discharging unit for Lithium ionbatteries at all temperatures including at low temperatures.

It is appreciated here that for Lithium battery charging low temperatureis intended to indicate those battery core temperatures at which DCcurrents (continuous or pulsed or other variations known in the art orthe like) causes damage to the battery or that the battery cannoteffectively be charged. In the Lithium ion battery discharging process,low temperature is intended to indicate temperatures at which theLithium ion battery discharge rate is significantly lower than itsnormal rate. In Lithium ion batteries the latter temperatures aregenerally lower than those for safe charging of the battery.

The unit 300 is powered by an external power source as shownschematically by arrow 302, which might for example be an outletprovided outdoors for charging the Lithium ion batteries of an electriccar. A microprocessor-based controller 304 (alternatively referred toherein and in FIG. 13 as a “control unit”) is used for determining thestatus of the battery 301 which may or may not have an internal orexternal temperature sensor 303 as was previously discussed while beingcharged and which when its battery core is determined to be below a safecharging temperature would instruct the AC and DC current generator 306to output high frequency AC current, shown schematically by arrow AC307) and when it is safe to charge, would instruct the AC and DC currentgenerator 306 to output DC current, shown schematically by arrow DC 308using the indicated switching element 310. The control unit 304 may beprogrammed (the instructions of which may be stored in a memory providedin the unit 300 and accessible by the control unit 304) to increase theinternal temperature of the battery 301 a safe amount to allow thebattery 301 to be charged at faster rates. The high frequency AC and DCcurrents are generated by the indicated AC and DC current generator 306,which is powered from the unit input power 302, and which is in directcommunication with the control unit 306 as indicated by the arrow 312.The control unit 304 is also in constant communication with the AC andDC current switching element 310 and can determine if one or the otherof the AC or DC current needs to be turned on or off. In this embodimentonly one of the AC or DC current can be turned on simultaneously.

In the embodiment 300 of FIG. 13, when either the AC or the DC currentis turned on, the current is passed through a charging voltage, currentand impedance measurement and charging and discharging regulation unit314 as indicated by arrow 316 a, which is used to determine theaforementioned current, voltage and impedance measurements needed forthe control unit 304 to control the charging process as was previouslydescribed. The charging voltage, current and impedance measurement andcharging and discharging regulation unit 314 also regulates the chargingcurrent during the charging cycles and the discharging current duringthe discharging cycles as directed by the control unit 304 to ensureproper and safe operation of the battery 301 and the charging anddischarging unit 300. The charging and discharging connections betweenthe above charging voltage, current and impedance measurement andcharging and discharging regulation unit 314 and the Lithium ion battery301 are indicated schematically by arrow 316 b. The battery discharge isrouted through the AC and DC current switching element 310 as shownschematically by arrow 318. The control unit 304 is also incommunication with all the system units as shown in FIG. 13 as well asthe battery temperature sensor 303 if such a sensor is provided.Although shown separately, the charging voltage, current and impedancemeasurement and charging and discharging regulation unit 314 can beintegrated into the control unit 304.

Once the battery core temperature has reached a safe charging level, thebattery can then be charged using a DC current or any other currentlyavailable technique for example with or without charging pulses, etc.,that are well known in the art and are used for efficient and safecharging of Lithium ion batteries. Any one of the well-known methods forsafeguarding the discharging process may also be employed. Similarly,different hardware designs are also well known in the art and may beused in the design of the charging and discharging circuitry of this andthe following embodiments after the aforementioned safe core temperaturelevels (measured directly or via the aforementioned impedance relatedtechniques) have been reached for charging the battery and when thedesired core temperature (measured directly or via the aforementionedimpedance related techniques) has been reached for efficient discharge(usually in terms of fast discharge rates and lower internal losseswhich are higher at low temperatures).

A block diagram of an alternative embodiment of a microprocessorcontrolled lithium ion battery charging and discharging unit 320 for lowtemperatures is shown in FIG. 14. The embodiment 320 is intended for useas the means for just charging Lithium ion batteries at all temperaturesincluding at low temperatures when the battery core temperature is belowits safe charging temperature level. All components of the embodiment320 are the same as those of the embodiment 300 of FIG. 13 except thatin the embodiment 320, the charging voltage, current and impedancemeasurement and charging and discharging regulation unit 314 a ismodified to eliminate its discharging regulation function. The Lithiumion charging unit 320 functions as previously described to charge thebattery using a DC current (continuous or pulsed or other variationsknown in the art or the like) while the battery core temperature isabove its safe charging temperature as measured using one or more of thepreviously described methods. If the battery core temperature isdetermined to be below or approaching the battery safe chargingtemperature, then the charging DC current is disconnected and the highfrequency AC current is applied as was previously described for theembodiment of FIG. 13 to raise the battery core temperature above itssafe charging temperature. The core temperature measurement can be madeeither continuously or at short enough intervals of time to ensure thatthe battery core temperature does not drop below its safe chargingtemperature during its charging.

A block diagram of another alternative embodiment of the microprocessorcontrolled lithium ion battery charging and discharging unit 340 for lowtemperatures is shown in FIG. 15. All components of the embodiment 340are the same as those of the embodiment 300 of FIG. 13 except that inthe embodiment 340, the AC and DC current switching element 310 of FIG.13 is replaced by an AC and DC current mixing element 342. Depending onthe detail design of the charging voltage, current and impedancemeasurement and charging and discharging regulation unit 314 b, someroutine modifications may be made to its design to accommodate the mixedAC and DC current signals.

The operation of the microprocessor controlled lithium ion batterycharging and discharging unit 340 of FIG. 5 is similar to that of theembodiment 300 of FIG. 13 except for the following. In the embodiment300 of FIG. 13 and during a battery charging cycle, the unit 300 caneither apply a high frequency AC current or a DC current to the battery.During low temperature charging, the unit 300 applied the high frequencyAC current until a safe battery core temperature is reached. Thecharging DC current (continuous or pulsed or other variations known inthe art or the like) is then applied to charge the battery 301. In theembodiment 340 of FIG. 15, when the battery core temperature is belowits safe charging temperature, the unit will similarly apply a highfrequency voltage to the battery to raise its core temperature to a safecharging level. However, the provision of the AC and DC current mixingelement allows the embodiment 340 maintain the battery core temperatureat a safe charging temperature level when it is detected to be droppingclose to the safe charging temperature. Whenever such a condition isdetected, by adding the high frequency AC current to the charging DCcurrent, the core temperature is raised above its safe chargingtemperature. By continuous or frequent measurement of the battery coretemperature, the temperature can be maintained above the battery safecharging temperature and be continuously charged. This situation isregularly encountered when the Lithium ion battery is exposed to a verycold environment and particularly if the battery is relatively small andhas a geometrical shape in which the ratio of its surface area to volumeis relatively high such as in batteries that are relatively thin withlarge surface areas.

The high frequency AC current may also be applied to the battery 301during the discharging cycles when the battery core temperature is belowor is dropping to levels close to a predetermined optimal level forefficient discharge (usually determined in terms of achievable dischargerates and lower internal losses, which are higher at low temperatures).In this embodiment, the battery core temperature can be measured atleast periodically via temperature sensor(s) if provided and/or usingthe aforementioned impedance related measuring techniques.

A block diagram of an alternative embodiment of the microprocessorcontrolled lithium ion battery charging and discharging unit 360 for lowtemperatures is shown in FIG. 16. The embodiment 360 is intended for useas the means for just charging Lithium ion batteries at all temperaturesincluding at low temperatures when the battery core temperature is belowits safe charging temperature level. All components of the embodiment360 are the same as those of the embodiment 340 of FIG. 15 except thatin the embodiment 360, the charging voltage, current and impedancemeasurement and charging and discharging regulation unit 314 c ismodified to eliminate its discharging regulation function. The Lithiumion charging unit 360 functions as described for the embodiment 340 ofFIG. 15 to raise the battery core temperature to a safe chargingtemperature level, to be followed by charging using a DC current(continuous or pulsed or other variations known in the art or the like)while the battery core temperature is above its safe chargingtemperature as measured using one or more of the previously describedmethods. Then whenever the battery core temperature is detected to havedropped to close to its safe charging temperature, the control unit 304instructs the AC and DC current generator to add a high frequency ACcurrent to the charging DC current, thereby raising the battery coretemperature above the safe charging temperature. By continuous orfrequent measurement of the battery core temperature, the coretemperature can be maintained above the battery safe chargingtemperature while continuously charging the battery.

A block diagram of another alternative embodiment of the novelmicroprocessor controlled lithium ion battery charging and dischargingunit 380 for low temperatures is shown in FIG. 17. The embodiment 380 isintended for use as the means for keeping the core temperature of aLithium ion battery above a prescribed level for efficient dischargingat all temperatures including at low temperatures. All components of theembodiment 380 are the same as those of the embodiment 360 of FIG. 15except that in the embodiment 380, the charging voltage, current andimpedance measurement and charging and discharging regulation unit 314 dis modified to only provide discharge regulation and voltage, currentand battery impedance measurements functionality. While the battery 301is being used to power certain load, i.e., while electrical energy isbeing discharged from the battery, the high frequency AC current mayalso be applied to the battery whenever the battery core temperature ismeasured to be below or if it is dropping close to levels predeterminedto be optimal for efficient battery discharge (usually determined interms of achievable discharge rates and low internal losses, which arehigher at low temperatures). In this embodiment, the battery coretemperature can be measured at least periodically via temperaturesensor(s) 303 if provided or using the aforementioned impedance relatedmeasuring techniques.

In the embodiment 380 of FIG. 17, the high frequency AC currentproducing generator element 306 a is powered from an external source302. External powering of the AC current generator 306 a may benecessary in certain situations, for example when the charged batterycore is at such a low temperature that cannot provide enough power tothe AC current generator 306 a or that it cannot provide enough power toraise the core temperature to the required operating temperature inshort enough period of time. If such situations are not expected to beencountered, the AC current generator 306 a may be powered directly bythe Lithium ion battery 301 itself or after an initial external poweringperiod. The embodiment of FIG. 18 illustrates such a discharging controlunit 400 in which the AC current generator 306 a of the dischargingcontrol unit is powered by the battery 301 itself.

The embodiment 400 shown in FIG. 18 is similar in functionality anddesign to the embodiment 380 of FIG. 17 except for the source of ACcurrent generator powering. In the embodiment 400, the AC currentgenerator 306 a is powered from the device discharge power and ACgenerator powering control unit 402 as shown by the arrow 404. The ACcurrent generator 306 a is in direct communication with the systemcontrol unit 304 as shown in FIG. 18. The discharge power and ACgenerator powering control unit 402 gets its power from the battery viathe voltage, current and impedance measurement and dischargingregulation unit 314 a as indicated by arrow 406. The input and outputcurrents to the battery 301 are via the connection indicated by thetwo-way arrow 316 a. The battery discharge is through the dischargepower and AC generator powering control unit 402 as shown by thedischarging power arrow 318. The generated AC current is provided to thevoltage, current and impedance measurement and discharging regulationunit 314 a, which is in communication with the system control unit 304,for increasing the battery core temperature when it is or about to fallbelow a prescribed temperature level.

The embodiment 400 of FIG. 18 may also be provided with an externalsource of powering for its high frequency AC current generator similarto the embodiment 380 of FIG. 17. The device will then have thecapability of using the external power source, particularly as aninitial source of power to bring the battery core temperature to aprescribed level before switching to an internal mode of powering asshown in the embodiment of FIG. 18. Such a configuration is shown in theembodiment 420 shown in FIG. 19, which is similar in functionality anddesign to the embodiment 400 of FIG. 18 except for the source poweringthe AC current generator 306 a. In the embodiment 400 of FIG. 18, the ACcurrent generator 306 a is only powered by the arrow 404. However, inthe embodiment 420 of FIG. 19, the AC current generator 306 a also cantake energy from the external input power 302, and depending on thesituation, select one or both of the power sources to heat the battery301.

FIGS. 20 and 21 show flow charts for charging and discharging a lithiumion battery at any temperature. As discussed above, if it is determinedthat a battery needs to be charged, a measurement is obtained of theinternal temperature of the lithium ion battery at step S10. Adetermination is then made at step S12 as to whether the obtainedtemperature is lower than some predetermined threshold temperature atwhich the battery cannot be charged or cannot be efficiently charged. Ifsuch determination at step S12 is no, the method proceeds to steps S14and S16 to conventionally charge the battery. However, if thedetermination at step S12 is yes, the method proceeds to step S18 wherehigh frequency AC voltage current is input to the lithium ion battery toheat the interior thereof. Such process can loop back to step S10 alongroute S20, periodically or at some regular interval until thedetermination of step S12 is no, at which time the battery is chargedconventionally at steps S14 and S16 until fully charged or the processis otherwise terminated. Thus, In FIG. 20, while the battery's coretemperature is detected to be lower than a predetermined temperature, toavoid damage the battery, the heating procedure is executed until thecore temperature rises high enough.

In FIG. 21, a measurement is made at step S10 to obtain a measurement ofthe battery internal temperature. Similarly to FIG. 20, if the coretemperature is determined to be less than a predetermined temperature atstep S12, the battery is input with a high-frequency, AC voltage currentat step S18 to heat the interior of the battery. Such process loops backto step S10 via S20 as discussed above with regard to FIG. 20 until thecore temperature is determined to be above such predetermined thresholdtemperature at step S12, at which time the process continues to step S22to discharge the lithium ion battery conventionally to a load. Thus, ascan be seen at loop S24, while the battery's core temperature is low sothat the discharging efficiency is dropping, the heating procedure isalso executed until the core temperature rises above the predeterminedtemperature. Thus, the discharging at step S22 is not be interruptedduring the heating procedure at step S18.

In both FIGS. 20 and 21, the alternative steps discussed above fordetermining whether the battery core has too low a temperature (withoutthe use of a temperature sensor) and cannot be charged conventionallycan also be used, in which case step S12 determines whether the coretemperature is too cold based on such determinations and not on a directtemperature measurement. Of course, both determinations can be used andthe method can include logic for making the determination in step S12based on multiple inputs (e.g., the temperature measurement, the batteryimpedance as described above with regard to the first method and/or thevoltage across a small load with regard to the second method discussedabove).

It is appreciated by those skilled in the art that numerous variationsof the described designs shown by the block diagrams of FIGS. 13-19 arealso possible for performing the indicated functions. The disclosure ofthe indicated embodiments by no means is intended to limit theirimplementation only in the described manner, rather to demonstrate thevarious combinations of functionalities that can be incorporated in agiven design and their general purpose.

It is also appreciated that the means of controlling the operation ofthe disclosed embodiments can be with the use of a microprocessor basedcontrol unit. However, it is also appreciated that that the generalfunctions performed by the microprocessor may also be performed byappropriate electronics and logic circuitry. Similar circuitry designshave been developed for the control of various processes in the industryand commercially and may be designed for the control of the disclosedLithium ion battery charging and discharging devices for all temperatureoperation including low temperature operation.

Lastly, any of the above methods can be practiced without the initialdetermination of the core temperature of the energy storage device. Thatis, a conventional charging input can be used regardless of thetemperature of the energy storage device's core and such determinationcan be made while the charging input is being applied. In this case, thecore temperature determination can be made periodically and if thetemperature of the core is obtained (directly measured or assumed) isbelow the predetermined threshold that would hinder further charging orapproaching within some limit of the predetermined threshold, thealternative inputs discussed above for heating the internal componentsof the energy storage device can be superimposed over the charging inputor the charging input can be stopped and the alternative input applieduntil the charging input can be resumed, such as when the predeterminedthreshold is reached. The same can also be for the discharging methodsdiscussed above.

FIG. 22 illustrates the diagram of one embodiment of a heating circuitfor a battery or energy storage device 450, such as a Lithium-ionbattery or nickel metal hydride battery or lead-acid battery or otherrechargeable or non-rechargeable battery, and for super-capacitors ofvarious types. In the diagram of FIG. 22, the device 450 is shown as asingle battery, however, it may also be a super-capacitor or more thanone serially or in parallel connected batteries or super-capacitors.

As can be seen in FIG. 22, an external power source is used to apply apositive current flow (indicated by the positive voltage V+) into thebattery 450 through the switch “SW1”. A resistor “R SINK” is used todraw current from the battery through the switch “SW2”. The signal foropening and closing the switches SW1 and SW2 are provided by thecontroller.

In this embodiment, the previously described high frequency AC voltagethat is applied to the battery 450 to heat its electrolyte is providedby the proper on/off switching of the switches SW1 and SW2 as follows.The process consists of applying a current into and drawing current outof the battery at the desired (high enough) frequency, to effectivelyshort the equivalent capacitor C_(s) (FIG. 11) in the case of theLithium-ion batteries as described by the model of FIG. 11, and theequivalent capacitance between the electrodes of other types ofbatteries and for the super-capacitors. For the super-capacitors, themodel of FIG. 1 may be made more detailed by separating the overallcapacitance C of FIG. 1 into a capacitor C, which essentially describesthe electrical energy that is stored as chemical energy, and a parallelcapacitor C_(s), which essentially indicates the capacitance between thedevice electrodes.

In the above process of passing a high frequency AC current through thebattery 450, FIG. 21, when the switch SW1 is closed, the switch SW2 isopened and vice versa. The switching signals to enable or disable theSW1 and SW2 are sent by the controller. The controller can be a circuitbased on a microcontroller, a combinational logic circuit, a FPGA or thelike. The current flow into the battery during the positive cycle iscontrolled by varying the voltage level of the voltage source “V+”. Byincreasing the level of voltage “V+” would increase the current flowinto the battery 450. The amount of voltage drops and current flow fromthe battery is controlled by changing the resistance value of “R SINK”,i.e., by reducing the resistance of the resistor “R SINK”, the currentflow out of the battery 450 is increased. It is therefore appreciated bythose skilled in the art that the resulting effective high frequency ACvoltage becomes close to a square wave. In general, the voltage level“V+” needs to be balanced to get a nearly the same charge and dischargefrom the battery during each cycle of the AC voltage application. Inaddition, and as described later in this disclosure, since the batterycharacteristics changes with temperature, the provided controller isdesired to vary the characteristics of the said AC voltage applicationfor optimal rate of heating of the battery.

FIG. 24 illustrates a circuit diagram implementation of the embodimentof the battery heating circuit of FIG. 22. In the circuit of FIG. 22,the switch SW1 is implemented by a P-Channel MOSFET “M1” and the switchSW2 is implemented by an N-Channel MOSFET “M2”. The resistors R1 and R2are pull-up and pull-down resistors required to properly bias the gateinput of the MOSFETs. The MOSFET M1 acts as a closed switch while M2acts as an open switch when the voltage level of the control signal VG1and VG2 are both at 0 V. The MOSFET M1 acts an open switch while M2 actsas a closed switch when the voltage level of the control signal VG1 isabove the gate-source threshold voltage of M1 and VG2 is above thegate-source threshold voltage of M2. To disable both switches when theheating circuit is not used, VG1 is set to above the gate-sourcethreshold voltage of M1 and VGS is set to be 0 V. Alternatively,disconnecting the circuit from the voltage source V+ can also disablethe switches.

It is appreciated by those skilled in the art that the implementation ofthe circuit diagram of FIG. 22 as shown in FIG. 24 is not unique andthat many other circuits that with the same functionality may bedesigned and that the circuit example of FIG. 24 is not intended toexclude any other circuits that can provide the same functionality.

FIG. 25 illustrates a circuit diagram of the embodiment of FIG. 24 witha provided controller that uses a temperature sensor input to activatethe battery heating circuitry when a prescribed low temperaturethreshold is detected. The device is shown to be provided with atemperature sensor, which is used to detect the battery temperature. Thecontroller consists of a microcontroller. The outputs voltage level ofthe temperature sensor is usually designed to be proportional to thebattery temperature being measured. The microcontroller monitors theoutput voltage of the temperature sensor using one of the internal ADCchannels “A1”, FIG. 25. When the temperature voltage output is below acertain preset threshold value, the microcontroller applies the drivingsignals to M1 and M2 as was previously described for the embodiment ofFIG. 24, therefore initiating the battery heating process. The drivingsignals are sent to the gate terminals of M1 and M2 though two digitaloutput pins D1 and D2 respectively. The microcontroller by be programmedto change the switching frequency of M1 and M2, i.e., the frequency ofthe heating current), depending on the measured battery temperatures asdescribed later in this disclosure.

The temperature sensor can be a low-voltage temperature sensor IC suchas the TMP35, a thermocouple module, a Resistance Temperature Detector(RTD) or a thermistor. The battery temperature is generally measured atthe battery surface, in which case during the described heating process,the battery core temperature is generally higher than the measuredsurface temperature. For relatively small batteries, e.g., those with adiameter of up to 1 inch, the difference may not introduce any issuesince the difference may be only a few degrees C., and the temperaturethreshold for low temperature may be set a few degrees lower than thedesired threshold to account for this difference. Alternatively,particularly for larger batteries and super-capacitors, a thermal modelof the battery may be used together with the time history of the heatingenergy input into the battery to estimate average (or peak high or low)internal temperature of the battery core and use that for setting thesaid controller low temperature threshold for switching the heatingcircuit on and off. Thermal modeling of batteries and super-capacitorsare well known in the art and for the present embodiments only a verysimplified model would generally suffice. A modeling technique that isspecifically tailored for use in Lithium-ion and other similar batteriesand in super-capacitors is described later in this disclosure.

It is appreciated by those skilled in the art that the usual practicefor temperature threshold setting would be to set a range oftemperature, below which heating process is turned on and above which itis turned off.

When an outside AC power source is used to power the circuit of FIG. 24or 25, an AC to DC converter and voltage regulator shown in the dashedline box in FIG. 25 may be used to supply the voltage V+ to the circuitof FIG. 24 and as well as for powering the microcontroller andtemperature sensor for the circuit of FIG. 25. The AC to DC converterand the voltage regulator may be integrated into the same circuit boardwith the rest of the components of the circuits or may be designed as anexternal component.

FIG. 26 illustrates the circuit diagram shown in FIG. 25 with thetemperature sensor implemented by using a thermistor or an RTD. Thethermistor can be either an NTC or a PTC type thermistor. The thermistorand the RTD resistance are proportional to the temperature. Therefore,the resistor R3 in series with either a thermistor or an RTD forms avoltage divider. The voltage measured by the microcontroller ADC channelA1 is therefore proportional to the temperature measured. The resistancevalue of R3 can be adjusted for different sensitivity.

FIG. 27 illustrates another embodiment of a battery heating circuitutilizing dual polarity power supplies V+ and V− to apply both positiveand negative current flow into the battery. When the P-Channel MOSFET M1is enabled while the N-Channel MOSFET M2 is disabled, the positivevoltage source V+ is connected to the positive terminal of the batteryand the current flows from the source into the battery. The voltagelevel of V+ must be larger than the voltage across the battery. When M2is enabled while M1 is disabled, the negative voltage source V− isconnected to the positive terminal of the battery and the current flowsfrom the battery into the source. The voltage level of V− is preferablylower than the voltage across the battery to balance the current flow.Resistors R1 and R4 are used to ensure the M1 and M2 are both disabledwhen the control signal voltage is 0 V. Resistors R2 and R3 can be usedto adjust the output DC offset voltage value. The control signal fromthe controller is AC coupled through a capacitor C1. When the controlsignal voltage is positive, M2 is enabled and M1 is disabled. When thecontrol signal voltage is negative, M1 is enabled and M2 is disabled.

FIG. 28 illustrates a circuit diagram of the controller with the circuitdiagram shown in FIG. 27. The controller consists of a temperaturesensor and a microcontroller. The temperature sensor is used to monitorthe temperature of the battery 450, which to be heated if below aprescribed temperature threshold. The outputs voltage level of thetemperature sensor is proportional to the battery temperature. Thetemperature sensor can be a low-voltage temperature sensor IC such asthe TMP35, a thermocouple module, a Resistance Temperature Detector(RTD) or a thermistor. The microcontroller monitors the output voltageof the temperature sensor using one of the internal ADC channels “A1”.When the temperature voltage output is below a certain preset thresholdvalue, the microcontroller applies the control signals to M1 and M2,therefore, initiating the heating process as was previously described.The control signals are sent to the gate terminals of M1 and M2 thoughdigital output pin D1. The AC coupled through the capacitor C1 allowscontrol signal voltage level at the gate terminal of M1 and M2 to beboth positive and negative while the digital pin D1 outputs a voltagevalue between 0 V and a positive preset value. The microcontroller canchange the switching frequency of M1 and M2 at different batterytemperatures if as is described later, particularly when the battery isintended to operate at very low temperatures, e.g., below −40 degrees C.The AC to DC converters 1 and 2 are used to supply the positive andnegative voltage source for the heating process, as well as for poweringthe microcontroller and temperature sensor though a voltage regulator.The AC to DC converters and the voltage regulator can be integrated intothe same circuit board with the rest of the components or they can beexternal components.

FIG. 29 illustrates the block diagram of another embodiment of thebattery 450 heating circuit utilizing a single power supply to applyboth positive and negative current flow into the battery 450. Fourswitches SW1A, SW1B, SW2A and SW2B are used for this purpose. Theswitches can be implemented by relays, semiconductor switch ICs orMOSFETs. When SW1A and SW1B are closed while SW2A and SW2B are open, thepositive voltage source V+ is connected to the positive terminal of thebattery 450 while the circuit ground is connected to the negativeterminal of the said battery. The current then flows from the sourceinto the battery 450. When SW2A and SW2B are closed while SW1A and SW1Bare open, the positive voltage source V+ is connected to the negativeterminal of the battery 450, while the circuit ground is connected tothe positive terminal of the said battery. Then the current flows fromthe battery 450 into the source. The voltage level V+ is preferablylarger than the voltage across the battery 450. A controller is used todrive all four switches at the proper sequence and frequency.

FIG. 30 illustrates a circuit diagram of the battery heating controllerwith the circuit of the embodiment of FIG. 29. The switches areimplemented by MOSFETs M1A, M1B, M2A and M2B representing SW1A, SW1B,SW2A and SW2B, respectively. The controller is a microcontroller and isprovided with a temperature sensor. The temperature sensor is used tomonitor the temperature of the battery 450. The outputs voltage level ofthe temperature sensor is proportional to the battery temperature. Thetemperature sensor can be a low-voltage temperature sensor IC such asthe TMP35, a thermocouple module, a Resistance Temperature Detector(RTD) or a thermistor. The microcontroller monitors the output voltageof the temperature sensor using one of the internal ADC channels “A1”.When the temperature voltage output is below the prescribed thresholdvalue, the microcontroller initiates the battery heating process byapplying the control signals from digital pins D1 and D2 to the MOSFETsthrough a driver circuit consists of Resistor R1 to R4, MOSFET M3 andM4. The driver circuit ensures the M1A, M1B, M2A and M2B can becompletely driven into cut-off mode (open) or saturation mode (closed)regardless of the difference voltage level between the control signalsvoltage and the source voltage of V+. When digital pin D1 is at logichigh while D2 is at logic low, M1A and M1B act as closed switches whileM2A and M2B act as open switches. Therefore, current flows from thesource into the battery 450. When digital pin D1 is at logic low whileD2 is at logic high, M1A and M1B act as open switches while M2A and M2Bact as closed switches. Therefore, current flows from the battery 450into the source. The frequency of the switching, i.e., the frequency ofthe applied current (AC heating current) is therefore set and controlledby the controller and may be varying as a function of the batterytemperature as is described later in the disclosure. An AC to DCconverter is used to supply the voltage source for the heating process,as well as for powering the microcontroller and temperature sensorthough a voltage regulator. The AC to DC converter and the voltageregulator can be integrated into the same circuit board with the rest ofthe components or they can be external components.

FIG. 31 shows an example of increasing the temperature of a standardmodel 18650 cell Li-ion battery, as measured on the outside surface ofthe battery, while it was heated from −30° C. to 20° C. using a circuitbased on the design shown in FIG. 27. The battery part number isLGABB418650.

As was previously described in this disclosure, the internal resistanceand inductance of Li-ion based batteries and in fact all rechargeableand primary batteries and super-capacitors vary by temperature, with thechanges becoming very significant at lower temperatures. As an example,FIGS. 32 and 33 are the plots of measured internal resistance andinternal inductance of a standard 18650 cell Li-ion battery (batterypart number is LGABB418650), respectively, in the temperature range of−55° C. to 45° C.

It is appreciated that as it is shown in the plots of FIGS. 32 and 32,since the internal resistance and inductance of the batteries andsuper-capacitors to be heated by the application of the described highfrequency voltage (current) vary significantly as a function oftemperature, particularly at very low temperatures at which achievinghigher heating rates is highly desirable. Therefore, the amplitude andfrequency of the applied high frequency voltage (current) must beadjusted for optimal heating rate as the temperature varies. In thevarious embodiments of the present invention this is readilyaccomplished by providing stored data, for example in the form of atable, in the controller and microcontroller of the embodiments of FIGS.22 and 24-30. It is appreciated by those skilled in the art that anexamination of the typical plots of FIGS. 32 and 33 shows that suchlook-up tables require only a very limited size due to the simple shapesof the plotted curves. In a more universal device, such look-up tabledata may also be stored in the controller and microcontroller memory fora wide range of batteries and super-capacitors that are commonly used.Alternatively, the user may be provided with the option of entering therelated look-up table data from using a number of data communicationmeans known in the art.

FIG. 34 illustrates another embodiment of a battery heating circuitutilizing a Push-Pull amplifier comprised of a PNP type Bipolar JunctionTransistor Q1 and a PNP type Bipolar Junction Transistor Q2. The baseterminals of both transistors are driven by the same control signalvoltage. When the signal voltage is positive, Q1 is activated while Q2is in cut-off mode and acts as an open switch. Current flows from thepositive voltage source V+ into the battery. When the signal voltage isnegative, Q2 is activated while Q1 is in cut-off mode and acts as anopen switch. Current flows from the battery into the negative voltagesource V−. The control signal is sent from a controller which is similarto the control circuit shown in FIG. 28. The controller outputs digitalpulses through AC coupling capacitor C1. The AC coupled control signalis then amplified by a device such as an Operational Amplifier U1. Theratio of resistors R1 and R2 is used to configure the voltage level ofthe output signal of U1. The AC coupled and amplified control signal isthen send to drive the transistors Q1 and Q2.

It is appreciated by those skilled in the art that the switchingcircuits of the embodiments of FIGS. 22 and 24-30 produce a nearlysquare wave shaped voltage input for battery and super-capacitorheating. Such square wave shaped high frequency voltages are effectivefor heating the various indicated batteries, including Li-ion andlead-acid batteries and super-capacitors if they are produced at highenough frequencies as was previously indicated. IN certain applications,particularly when the battery or super-capacitor to be heated has highinductance, it may be desired to employ heating AC voltages that arecloser to being purely sinusoidal. For this purpose, as an example, theheating circuit of the embodiment of FIG. 34 may be modified asillustrated in FIG. 35. In this circuit, the resistor R3, and capacitorsC3 and C1 together forms a filter, which turns the square wavecontroller generated signal into an essentially sinusoidal signal.

FIG. 36 illustrates another embodiment of a battery heating circuitutilizing a Power Operational Amplifier Integrated Circuit U1. The PowerOperational Amplifier Integrated Circuit U1 can be configured asinverting or non-inverting amplifier. FIG. 36 illustrates an example ofU1 as configured as an inverting amplifier. In this embodiment, thecontrol signal is sent from a controller, which may be similar to thecontrol circuit shown in the embodiment of FIG. 28. The control signalis sent to the input of U1 via an AC coupling capacitor C1. The ratio ofresistors R1 and R2 is used to configure the voltage level of the outputof U1. The output power of U1 is then used to apply heating for thebattery via an AC coupling capacitor C2. The capacitor C2 is required toprevent damage to the output terminal of U1.

FIG. 37 illustrates a modified alternative of the battery heatingcircuit embodiment of FIG. 36. In this circuit, the resistor R3, andcapacitors C3 and C1 together forms a filter, which turns the squarewave controller generated signal into an essentially sinusoidal signal.

FIG. 38 illustrates a modified alternative of the battery heatingcircuit of the embodiment of FIG. 37. In this circuit, a transformer T1is used to provide impedance matching between the battery and the outputof the Power Operational Amplifier Integrated Circuit U1. Thetransformer T1 is necessary when the battery impedance is much smallerthan the output impedance of the Power Operational Amplifier IntegratedCircuit U1. The coil resistance of N1 inside T1 should be high enough tomaintain output efficiency of U1, as well as to reduce power dissipationwithin U1. Ac coupling capacitor C2 is also required to prevent the coilresistance of N2 from loading the battery.

It is appreciated that the battery heating circuit embodiments of FIGS.22, 24-30 and 34-38 use external power supply for their operation. Incertain applications, it is desirable for the battery heating circuit tooperate using power provided by the battery itself. For battery typessuch as Li-ion, NiMH and Lead Acid, the maximum output current that isavailable at the rated voltage is lower at lower battery temperatures.FIG. 39 is a typical plot showing the maximum output current levels of aLi-ion, a NiMH and a VRLA (Valve-Regulated Lead-Acid) batteries as afunction temperature. As can be seen in FIG. 39, the available currentdrops significantly at lower temperatures. For this reason, thefollowing battery heating circuit embodiments of the present inventionare divided into those for applications in which the battery can stillprovide enough current to directly power the heating circuit and thosein which the available current level is not high enough and requireintermediate storage. The two circuit types are desired to work togetherfor optimal performance, i.e. once the battery is heated enough so thatit can provide the required current levels, then the heating circuit isswitched to direct powering mode.

FIG. 40 illustrates another embodiment of a battery 450 heating circuit,which uses power from the said battery that is being heated directly,therefore the embodiment does not require an external power supply. Thecircuit embodiment of FIG. 40 is a modification of the basic heatingcircuit of the embodiment of FIG. 22. In the circuit of FIG. 40, thevoltage source V+ is provided by a step-up voltage regulator whichacquires the input voltage from the battery 450 terminals via a LCfilter comprised of an inductor L1 and a capacitor C1. The step-upvoltage regulator outputs a voltage level which is an increased voltagelevel of the input voltage. The LC filter allows the input voltage levelof the voltage regulator remains stable during the heating process whenthe current is flowing into and out of the battery alternatively. Thevoltage regulator requires a minimum amount of input current to maintainthe output voltage level and to provide enough current for the heatingprocess. The available current at rated voltage for a typical Li-ion,NiMH and Lead Acid battery is shown in FIG. 39. The circuit of FIG. 40is ideal for operating at a battery temperature above a certain valuewhich allows enough current for the heating process while maintainingthe voltage level of V+. For example, a Li-ion 28V battery pack is usedwith the circuit in FIG. 40 and the minimum required current for thecircuit in FIG. 40 to operate properly is around 5 A. Therefore, theminimum operating temperature for this example is −20° C. as shown inFIG. 39.

It is appreciated that the heating circuit embodiment of FIG. 40, whichis powered by the battery 450 itself, may also be provided with anexternal powering. As a result, the user will be able to use externalpower for heating the battery 450 when such an external power source isavailable, thereby saving the battery charges and accelerating thebattery heating process. In this case, the optional terminals of V+ andCircuit Ground can be wired to an external power supply. It isappreciated that once the battery temperature has increased up to anappropriate value, the external power supply can be disconnected, andthe subsequence heating process can be powered by the battery itself. Inmany such applications, the external power source is used to bring thebattery temperature to or close to room temperature or a temperaturethat the battery performance is near optimal or at the desired level,and then the external powering is terminated, and the battery power isused to maintain the battery temperature at the desired level.

Examples of such applications are vehicles or power tool batteries,where the vehicle or the power tool is stored in unheated garage orstorage where external power is available. Then the user would firstheat the battery in cold temperature and when it is at the desiredtemperature level, the external power is disconnected, and the batterytemperature is maintained at the desired level using the battery power.The user can then use the vehicle and power toll in very cold weatherwithout losing battery performance. It is appreciated by those skilledin the art that such applications are plentiful and includes mostdevices and systems that are used at one time or another in lowtemperature environments.

FIG. 41 illustrates the battery heating circuit embodiment of FIG. 40 asmodified to allow for operation at very low temperatures at which thebattery cannot provide high enough current for operation of the circuitdirectly from the battery itself. The battery heating circuit embodimentof FIG. 41 operates without external power. The voltage source V+ isprovided by a step-up voltage regulator which acquires the input voltagefrom the capacitor C2 via a LC filter comprised of an inductor L1 and acapacitor C1. The capacitor C2 is charged when the switch SW3 isswitched to position A. Once the capacitor is fully charged, thecontroller switches SW3 to position B and the voltage regulator drawsenergy from C2 to provide energy for the heating process. Once thevoltage across C2 drops to a certain level and no longer able tomaintain the operation of the voltage regulator, SW3 is switched toposition A and to be fully charged once again. This process repeatsuntil the controller senses that the battery temperature is above theprescribed threshold for direct self-powering. The battery can then beused to directly power the heating circuit as was previously describedfor the embodiment of FIG. 40.

FIG. 42 illustrates another embodiment of a battery 450 heating circuit,which uses power from the said battery that being heated directly,therefore the embodiment does not require an external power supply. Thecircuit embodiment of FIG. 42 is a modification of the basic heatingcircuit of the embodiment of FIG. 29. The voltage source V+ is providedby a step-up voltage regulator which acquires the input voltage from thebattery 450 terminals via a LC filter comprised of an inductor L1 and acapacitor C1. The step-up voltage regulator outputs a voltage level,which is higher than the input voltage level. The LC filter allows theinput voltage level of the voltage regulator to remain stable during theheating process when the current is alternatively flowing into and outof the battery 450. The voltage regulator requires a minimum amount ofinput current to maintain the output voltage level and to provide enoughcurrent for the heating process. The available current at rated voltagefor a typical Li-ion, NiMH and Lead Acid battery is shown in FIG. 39.The circuit in FIG. 42 is ideal for operating at a battery 450temperature that is above the level at which the battery can provideenough current for the heating process while maintaining the requiredvoltage level of V+. For example, a Li-ion 28V battery pack is used withthe circuit in FIG. 42 and the minimum required current for the circuitin FIG. 42 to operate properly is around 5 A. Therefore, the minimumoperating temperature for this example is −20° C. as shown in FIG. 39.

It is appreciated that the heating circuit embodiment of FIG. 42, whichis powered by the battery 450 itself, may also be provided with anexternal powering. As a result, the user will be able to use externalpower for heating the battery 450 when such an external power source isavailable, thereby saving the battery charges and accelerating thebattery heating process. In this case, the optional terminals of V+ andCircuit Ground can be wired to an external power supply. It isappreciated that once the battery temperature has increased up to anappropriate value, the external power supply can be disconnected, andthe subsequence heating process can be powered by the battery itself. Inmany such applications, the external power source is used to bring thebattery temperature to or close to room temperature or a temperaturethat the battery performance is near optimal or at the desired level,and then the external powering is terminated, and the battery power isused to maintain the battery temperature at the desired level. Examplesof such applications as vehicles or power tool batteries and othersimilar applications were previously discussed.

FIG. 43 illustrates the battery heating circuit embodiment of FIG. 42 asmodified to allow for operation at very low temperatures at which thebattery cannot provide high enough current for operation of the circuitdirectly from the battery itself. The battery heating circuit embodimentof FIG. 43 operates without external power. The voltage source V+ isprovided by a step-up voltage regulator which acquires the input voltagefrom the capacitor C2 via a LC filter comprised of an inductor L1 and acapacitor C1. The capacitor C2 is being charged when the switch SW3 isswitched to position A. Once the capacitor is fully charged, thecontroller switches SW3 to position B and the voltage regulator drawsenergy from C2 to provide energy for the heating process. Once thevoltage across C2 drops to a certain level and no longer able tomaintain the operation of the voltage regulator, SW3 is switched toposition A and to be fully charged once again. This process repeatsuntil the controller senses that the battery temperature is above acertain value. This process repeats until the controller senses that thebattery temperature is above the prescribed threshold for directself-powering. The battery can then be used to directly power theheating circuit as was previously described for the embodiment of FIG.42.

It is appreciated by those skilled in the art that in most applications,batteries and super-capacitors are housed in a closed environment, suchas a battery pack. In some applications, such as in the case oflead-acid batteries, the battery may not be positioned in a relativelyclosed housing. In all these applications, when the battery orsuper-capacitor is being heated using one of the above embodiments ofthe present invention, the temperature measured by a sensor that isattached to the outside surface of the battery or super-capacitor wouldgenerally be lower than that of the battery and super-capacitor core. Inall these applications, a thermal model of the battery orsuper-capacitor core, its housing (including insulation layer and/orpaint), and other covering layers can be used to predict the coretemperature by measuring the temperature of the battery andsuper-capacitor outside surface. In these models, the amount of inputheating energy and the measured outside surface temperature as afunction of time together with the initial temperature of the battery(usually the same as the temperature measured on the battery surface)are used to predict the battery or super-capacitor core temperature. Itis also appreciated by those skilled in the art that such a model can bereadily programmed into the processor of the controllers of the variousembodiments of the present invention.

Several methods and related circuits for generating the high frequencycurrent for direct heating of battery and super-capacitor core werepreviously described. It is, however, highly desirable that the deviceused to pass high frequency current through the battery be capable ofautomatically keep the high frequency current symmetric with no ornegligible DC component. Such a low temperature direct heating devicefor batteries and super-capacitors can then be used for any voltage andinternal impedance, both of which do vary with temperature, withoutrequiring the user or a separate circuitry with sensory devices toperform the task of making the required adjustments to achieve therequired negligible DC component of the high frequency heating currentthat is passed through the battery or super-capacitor.

The methods to be disclosed are herein described by examples of one oftheir possible circuit designs. It is appreciated by those skilled inthe art that the described methods may be implemented using othersimilar circuit designs.

FIG. 44 illustrates the block diagram of one embodiment of such a directbattery heating system. The heating system of FIG. 44 consists of a“heating engine” 501, which causes an oscillatory current 502 to flowthrough the battery 503. The “heating engine” is powered by a dualpolarity high current source 504, for example a source providing 50-150amps. A “slave” microcontroller 505 is programmed to provide voltagepulses for alternating operation of the push and pull MOSFET switches orthe like of the “heating engine” 501, an example of which is shown inFIG. 45 and is described later in this disclosure. The “slave”microcontroller 505 is enabled by a “master” microcontroller 506, whichutilizes sensory inputs 507 from the battery to provide digital controlof the “heating engine” 501. The functions of the “master” and “slave”microcontrollers may be performed by a single microcontroller.

Typically, one or more temperature sensors 508, for example an NTCthermistor or the like, monitor the battery temperature. A currentsensor 509 may also be provided to measure the RMS value of the heatingcurrent. The heating cycle is initiated whenever the battery temperaturefalls below the desired operational temperature and disabled wheneverthe battery temperature exceeds the upper set limit. Normal operation ofthe heating system maintains the battery temperature within the desiredlimits.

It is appreciated that due to unpredictable events a potentiallyhazardous condition such as the battery temperature passing a certainpreset threshold is detected. In addition to the normal control of the“heating engine”, a software generated signal may also be provided fordisabling the “heating engine” whenever the measured temperature fallsoutside the normal range of operation or a command is received from someexternal source (not shown). The system may be programmed toautomatically recover when the temperature drops below the hazardouscondition. However, if the software has been compromised, a hardwareshutdown circuit 510 may be provided to detect the temperature passingthe preset threshold and disable the high current power supplies. The“heating engine” remains in the OFF position until the systemreactivated.

FIG. 45 illustrates the operation of the “heating engine” 501, whichcomprises of a gate-driver module 511, voltage controlled toggleswitches 512, for example solid-state relays or the like, plurality ofN-type MOSFETS 513 arranged in a parallel configuration, plurality ofP-type MOSFETS 514 arranged in a parallel configuration, and pluralityof capacitors 515 arranged in a parallel configuration. Circuitoperation is independent of the battery voltage and chemistry. The slavemicrocontroller 505, FIG. 44, generates the control waveform 516 for thebank of N-MOSFETs 513 and control waveform 517 for the bank of P-MOSFETs514. The control waveforms 516 and 517 are converted to the positive 518and negative 519 gate to source voltage requirements of N- and P-typeMOSFETS 513 and 514, respectively. These switching pulses are passed tothe respective gate terminals 520 and 521. The N-type MOSFETs 513provide current flow into the positive terminal of the battery. Duringthe conduction (ON) of the p-type MOSFETS 514 the current flows out ofthe positive terminal. Typical switching waveforms 516 and 517 and thebattery current waveform 521 are illustrated in FIG. 46. Furthermore, animportant and innovative feature of the heating cycle is the OFF period523 when both channel MOSFETs are in the OFF mode. This added featureeliminates a potentially hazardous condition forcing both the P- andN-type MOSFETs to the ON state at the same time.

With reference to FIG. 45, the parallel bank of capacitors 515 providesa distinct functional advantage for the heating system. In the absenceof the capacitor bank, the positive and negative supply voltages need tobe independently adjusted in order to obtain a symmetrical heatingcurrent flow through the battery. Subsequently, power supply voltagerequirements become dependent on the battery open circuit voltage,adding significant complexity to the design of the heating system.However, as illustrated in FIG. 48 and expressed in equation (4) anddescribed in detail later in this disclosure, with the present noveldesign and as it is described below, with the inclusion of the capacitorbank 515, symmetrical current flow through any battery is guaranteed bythe design. With this novel design, the disclosed “heating engine” canthen be used to heat single cells or cell packs of various batterychemistries, such as lead-acid, Li-ion, Li-polymer, and others.

Another important consideration for the disclosed high frequency directheating of batteries and super-capacitors is the efficiency of theheating circuit. Poor efficiency translates into excess heat beinggenerated by the electronic components, requiring the means of totransport a significant amount of heat away from the circuit components.

The heating efficiency of the circuit is given by the ratio of theeffective battery resistance to the total resistance of the circuit atthe operation frequency and can be expressed as,

$\begin{matrix}{\eta_{heating} = {\frac{R_{bat}}{R_{bat} + R_{cir}} = {1 - \frac{R_{cir}}{R_{tot}}}}} & (3)\end{matrix}$

where R_(bat), R_(cir), and R_(tot), are the battery resistance, thecircuit resistance, ant total resistance, respectively. The circuitresistance is a sum of the MOSFET (N or P) ON resistance, the equivalentseries resistance of the capacitor and all other parasitic resistances.It can be appreciated that a plurality of MOSFETs and capacitors reducethe circuit resistance in a proportional manner. Thus, for any givenbattery resistance, particularly, for battery chemistries such asLi-poly or lead-acid which have resistance in the few milli-ohm range,it is possible to obtain heating efficiencies approaching unity. Forexample, a circuit with a single capacitor with a resistance of 7 mΩ anda single N-MOSFET that has an ON resistance of 10 mΩ yields a heatingefficiency of around 64% for a battery with an internal resistance of 30mΩ at a given temperature. However, by using a bank of five shunting ofthe above capacitors and MOSFETs, the heating efficiency increases to90%.

While the above efficiency calculations are based on conduction losses,it is appreciated that at higher operational frequencies (order of MHz),switching losses would also be higher.

FIG. 47 shows the schematic of one possible implementation of thehardware shutdown circuit 510, FIG. 44, which is designed to cut-offpower to the “heating engine” 501 in FIG. 44 when higher than a presettemperature threshold is detected. Output from the battery temperaturesensor 524 is compared with the set-point 525 for this condition. Outputof the comparator 526 switches to a high level indicating a higher thana preset temperature condition has been detected. Two AND gates 527 and528 produce outputs 529 and 530, according to the truth table 531. Thetwo outputs 529 and 530 drive an exclusive OR gate 532, which produces alogic LOW at the output 533 for normal operation. The hardware shutdowncircuit ensures that the “heating engine” is powered only if the higherthan preset temperature signal is FALSE. It is appreciated that thehardware shutdown circuit 510 may also be implemented by alternativelydesigned circuits with and without programmable microprocessors.

The “heating engine” 501 (FIG. 44) operation can be analyzed in threedistinct time regions: 1) N-type MOSFET ON and P-Type MOSFET OFF(positive current); 2) Both MOSFETs are OFF; and 3) N-type MOSFET OFFand P-Type MOSFET ON (negative current). Operation in Regions (1) and(3) are similar with the exception of the current polarity reversal.Thus, analysis need only be performed in either Region (1) or (3).During the positive cycle, the N-Type MOSFET is ON having an equivalentresistance Rory. With reference to FIG. 45, the current i(t) flowingthrough the battery, during the conduction time T, is given by,

$\begin{matrix}{{i(t)} = \left\{ \begin{matrix}{\frac{V_{s}}{R}{\exp\left( {- \frac{t}{\tau}} \right)}} & , & {0 \leq t \leq T} \\{\frac{V_{s}}{R}\left( {1 - {\exp\left( {- \frac{T}{\tau}} \right)}} \right){\exp\left( {- \frac{t - T}{\tau}} \right)}} & , & {t \geq T}\end{matrix} \right.} & (4)\end{matrix}$

FIG. 48 shows the complete current waveform 534 over one cycle when R=50mΩ, C=2 mF and V_(s)=±3.3 V. T is the ON time for both MOSFETs and τ=RCis the time constant of the heating circuit. Transition between thepositive and negative current flow is separated by the OFF state 535 ofboth MOSFETs. FIG. 48 shows the current waveform for threeconditions: 1) dashed line 536 is the response when τ=0.1T (R=50 mΩ,C=0.2 mF; 2) solid line 534 when τ=T (R=50 mΩ, C=2 mF); and 3) dash-dotline 537 when τ=10T (R=50 mΩ, C=20 mF). It is noted that while the shapeof the response is different for the three conditions, however, theaverage current through the battery is zero. From a practicalperspective it is desirable to operate the heating engine close to thelatter condition τ=10T.

FIG. 49 shows the actual measured current response during the heating ofa 12 V Type 31 lead-acid battery 538 commonly used in trucks. In thiscircuit, peak currents of 70 A were measured.

The above description of the heating system has focused on arechargeable battery merely for convenience. It is appreciated that thesame heating system can be used for heating charged or unchargedsuper-capacitors and all primary batteries, including liquid reservebatteries and thermal reserve batteries at low temperatures.

FIG. 50 illustrates the circuit diagram of the first high efficiencyself-heating device embodiment of the present invention. This device isdesigned to maintain a battery at a desired operating temperature whenthe ambient temperature drops a prescribed amount below the desiredoperating temperature.

As can be seen in FIG. 50, the battery (providing a voltage VB) isplaced in series with an external capacitor C and an inductor L to forma series resonance circuit, loop “A”. In the circuit of FIG. 50, theresistor RB indicates the internal resistance of the battery to highfrequency current as was previously described for high frequency heatingof batteries and super-capacitors. With the switch S2 open, the switchS1 is suddenly closed. The resonant circuit of loop “A” will then passan oscillating current through the battery resistor at the resonantfrequency of the circuit, thereby heating the battery core, primarily byheating its electrolyte as was previously described for previous highfrequency battery heating embodiments. The amplitude of oscillatorycurrent will diminish as the oscillatory energy is converted to heat andresonance circuit reaches a steady state condition with a heatingcurrent which goes to zero as the capacitor is charged to the batterypotential. At this time, the switch S1 is opened and the switch S2 isclosed. The electrical energy stored in the capacitor C is discharged tothe ground. The switch S2 is then opened and the heating cycle isrepeated as needed until the prescribed battery temperature is reached.

The steady state time constant of the circuit is a function of theeffective series resistance (hereinafter indicated as R_(tot), of thebattery and all other resistance arising from of the reactive componentsand other parasitic resistances (not shown in FIG. 50 as expected to besignificantly lower than RB for a properly designed circuit). The peakcurrent and the resonance frequency of the loop “A” circuit aredetermined by the ON switching time of the switch S1 and the values ofC, L and R_(tot).

FIG. 51 shows the block diagram of such a high efficiency self-heatingdevice for batteries and super-capacitors. The elements in the indicatedbox with dashed lines 539 represent the battery and its in-seriesinternal resistance to high frequency current. The battery is shown tobe provided with a temperature sensor (a thermistor in FIG. 51), theoutput of which provided the means for the microcontroller to initiatethe heating cycles as was described above when the battery temperaturedrops below a preset temperature level and cease the heating processwhen the preset upper battery temperature has been reached. TheSwitching Network block in FIG. 51 represent the components of theswitches S1 and S2 of FIG. 50 as operated by the device microcontroller.

FIG. 52 shows one implementation of the block diagram of the highefficiency self-heating device for batteries and super-capacitors ofFIG. 51, as used for self-heating a battery indicated by the dashed linebox 540. In the box 540, VB indicates battery as the voltage source withan internal resistance RB to high frequency currents. The self-heatingdevice is intended to heat the battery in a cold environment to keep itwithin a prescribe range of temperature, defined as an upper temperatureand lower temperature limits. As was described for the circuits of FIG.51, the battery is provided with a temperature sensor 541 that measuresthe battery temperature using the “temperature sensor circuit”, whichprovided the measured temperature signal 542 to the devicemicrocontroller. A series resonant circuit is formed by the batteryinternal resistance to high frequency current RB, external inductor Land capacitor C. The battery 540 powers the microcontroller and thetemperature sensor circuit.

In the battery self-heating device embodiment of FIG. 52, thetemperature sensor circuit generates a controller signal 542 to startand stop the self-heating cycle by comparing the measured temperature tothe desired operating temperature range. When the battery is to beheated, the microcontroller initiates a toggling heating cycle bygenerating control signals V_(s1) and V_(s2) for switches S1 and S2,respectively. The switching function is achieved by using of N-MOSFETSS1 and S2, or the like. The resistors R1 and R2 are used for properaction of the N-MOSFET switches. Upon receiving a heating request fromthe temperature sensor circuit, that is, when the measured temperaturefalls below the set threshold, the microcontroller sends a controlsignal V_(S1) to turn on (close) switch S1 and a control signal V_(S2)to turn off (open) switch S2. With this configuration of switches thebattery 540 and the series combination of RB, L and C members forms aseries resonant circuit under a forced response, operating in theunder-damped regime. The flow of high frequency sinusoidal currentthrough the series RB, L and C resonant circuit, in particular, throughthe internal resistance RB, results in generation of heat within thebattery core as was described for high frequency battery heatingembodiments, thereby causing the battery core temperature to rise. Oncethe capacitor C is charged close to the voltage of the battery VB, theswitch S2 is closed and switch S1 is opened. The charges collected inthe capacitor C1 are discharged to the ground and the heating cyclesrepeated. Then as the battery core temperature increases to the setupper temperature limit for the battery, the temperature sensor circuitsends a control signal 542 to the microcontroller to stop the heatingcycle. In summary, the self-heating cycle comprises of a series ofcontrolled switching (toggling) cycles with switch S1 closed and switchS2 open during the resonant charging of the capacitor C and a rapiddischarge of the capacitor C by closing switch S2 momentarily andopening switch S1. The switching sequence is repeated until the batterycore reaches the prescribed temperature, usually at or close to theprescribed upper temperature limit.

The heating efficiency η of the self-heating device circuit of FIG. 52is given by the ratio of the effective battery resistance RB at the(high frequency) resonance frequency (loop “A” in FIG. 50) to the totalresistance of the circuit (not shown in FIGS. 50-52), that is,

$\eta = {\frac{RB}{{RB} + R_{L} + R_{C} + R_{W}} = {1 - \frac{R_{cir}}{R_{tot}}}}$

where R_(bat), R_(L), R_(C) and R_(w), are the series resistances of thebattery, inductor, capacitor and all connecting wires, respectively, atthe resonance frequency, the total of which is the circuit resistanceR_(cir). The total circuit resistance R_(cir) can be estimated from thecomponent data sheets and the total resistance (R_(tot)=R_(cir)+R_(bat))can be determined from the measured values of the current flowingthrough the battery and the voltage across the battery. Through carefulselection of the reactive components, the circuit heating efficiency canbe made arbitrarily high by insuring that R_(cir)<<R_(tot). Theadditional loss due to the discharging of the capacitor C is generallylow and around 5-10 percent of the total energy.

As an example, the heating efficiency of the self-heating deviceembodiment of FIG. 52 was used on a Lithium ion cell (ModelLGABB418650), as placed in an environmental chamber that was set tolower its temperature from 20° C. to −40° C. The battery was wrapped ina 1 mm thick thermal battery insulation layer. The temperature of thebattery was set to be maintained between 20° C. and 25° C.

In the self-heating device embodiment of FIG. 52, a switching frequencyof 2 kHz was used for the switch S2, with a discharge pulse width of 100μs. The instantaneous voltage and current measurements were used toestimate the total resistance of the circuit during the heating cycle.In this example, the resistances are R_(L)=7 mΩ, and R_(C)=4 mΩ, and apeak value of resistance R_(tot)=169 mΩ was calculated using the RMSvalues of the voltage and current waveforms. These parameters give acircuit heating efficiency of 93%, which includes the capacitordischarge loss.

At the end of each 500 μs (2 kHz) resonance heating cycle, the storedenergy in the capacitor is dissipated through a short circuit over 100μs. In the above test example, the stored energy in the capacitor, after400 μs of heating, was 0.68 mJ. During the heating time the batterysupplied a total of 34.8 mJ. That means ˜2% of the supplied energy isstored in the capacitor at the end of heating pulse.

FIG. 53 shows the plot of the temperature of the environmental chamber545 as a function of time within which the battery of this example wasplaced. The set battery temperature T_(set) is shown with the dash anddot line. The measure temperature of the battery during the self-heatingportion 543 and cooling portion 544 (when the self-heating device ifturned off) are also shown. The plot 546 is the oscilloscope picture ofthe actual measured high frequency current that is passed through thebattery, i.e., the battery high frequency resistance to current RB, thatheats the battery core.

In the self-heating device embodiments of FIGS. 50-52, the energy storedin the capacitor C is lost, thereby reducing the aforementioned circuitheating efficiency from 93% to around 91%. The electrical energy storedin the capacitor C may however be used to supplement the heating of thebattery, particularly for most Li-ion or Li-polymer or the likebatteries in which most batteries are packed with several cells that areconnected in series or in parallel or their combination to obtain thedesired battery voltage or operating current. It is appreciated by thoseskilled in the art that in such batteries, temperature sensors arepositioned between the battery packs to measure the battery temperaturesfor thermal control purposes or for battery heating using one of thedisclosed embodiments of the present invention, including theself-heating device embodiment of FIGS. 50-52.

It is appreciated that since battery cells in a battery pack are neverexactly identical, therefore they generally have to be individually (orin pairs or in certain configuration) monitored for thermal controlpurposes as well as for heating using one of the disclosed embodimentsof the present invention, including the self-heating device embodimentof FIGS. 50-52. For this reason, the charges stored in the capacitor C,may be dissipated in a provided resistor R_(H) as shown in FIG. 54 oncethe switch S2 is closed. The circuit of FIG. 54 is identical to that ofFIG. 52 except for the addition of the resistor R_(H) and operates thesame as the embodiment of FIG. 52 as was previously described, with onlydifference being that instead of the electrical energy stored in thecapacitor C during each cycle of battery heating being wasted, it isused to heat the resistor R_(H), which is positioned between batterycells of a battery pack. Thereby, the generated heat is used to heat thebattery (even though from its outside shell). It is appreciated that ingeneral thin and flat resistors (similar in thickness to the temperaturesensors being used) are preferred to be used for the resistor R_(H) sothat the total battery pack volume is not increased.

In the above self-heating device embodiments of the present invention,the high frequency heating current that is applied to the battery isgenerated by the described switching circuits that are powered by thebattery power. In the following embodiments of the present invention, anovel method is described that can be used to design self-heatingdevices for almost all batteries, such as Li-ion, Li-polymer, Lead acid,NiMH, and other primary and rechargeable batteries. The resultingself-heating devices are simpler in design, have significantly fewercomponents, and highly efficient in performing the battery core heatingwith minimal electrical energy loss.

FIG. 55 shows the circuit schematic of such a self-heating device, whichis significantly simpler in design and is constructed with fewercomponents. The self-heating device is designed to maintain the batterycore operational temperature close to a prescribed temperature in coldtemperature environments using the battery power. In the circuitschematic of FIG. 54, the battery 601 (as shown inside the rectanglewith dashed lines) is modeled as an ideal voltage source 602, with anopen circuit voltage V_(B), an internal resistance 603 (R_(B)) and aninternal inductance 604 (L_(B)). The self-heating circuit is initiatedby a control signal 605, which is generated by a temperature sensorcircuit 606 when the reading of the temperature sensor 607 is below theset operational temperature.

The heating circuit is disabled when the measured temperature is abovethe set operational temperature. The illustrated self-heating circuithas three operational phases, which are described with references toFIGS. 55 to 59. The signal 605 initiates the execution of a programmedsequence of timing waveforms which control the operation of electronicswitches 608 (S₁) and 609 (S₂). The signal 610 controls the opening andclosing of the electronic switch 608 and the signal 611 controls theopening of the electronic switch 609. Correct timing of these controlsignals is essential for proper operation of the battery self-heatingsystem. The microcontroller 612 processes the heat ON/OFF signal 605 togenerate the timing waveforms for the electronic switches 608 and 609.The self-heating system is designed to operate autonomously, withoutrequiring any external power source or external control signals.Further, the self-heating system can provide heating to the batterywhile it is mounted in the vehicle and when the vehicle engine and/orother electrical and electronics are on.

The self-heating circuit of FIG. 54 generates heat in the core of thebattery through the high-frequency oscillatory current following throughthe forced series resonance circuit formed by the battery voltage source602, the internal resistance 603 (R_(B)), the internal inductance 604(L_(B)) and an external capacitor 613 (C). At the start of the heatingcycle switch 608 is open and switch 609 is momentarily closed todischarge the capacitor 613. The heating phase is initiated by openingswitch 609 and closing switch 608. The resonant heating described belowcontinues until the capacitor 613 is charged to the battery open-circuitvoltage, at which point the current i₁ goes to zero and the heatingstops.

The duration of the heating time is determined by the component values.For example, the plot (a) in FIG. 56 shows the expected current waveform614 flowing through the series resonant circuit, and plot (b) in FIG. 56shows the voltage waveform 615. These plots are generated for a 12 Vlead-acid battery with R_(B)=2 mΩ, L_(B)=7 mH and C=226 μF. After a fewoscillations, the current (i₁) goes to zero indicating the capacitor hasbeen fully charged to the voltage level 616, corresponding to the opencircuit voltage of the battery.

Referring to FIG. 55, it is appreciated that continued heating of thebattery requires discharging of the capacitor 613 which can be achievedby opening switch 608 and closing switch 609 through a resistive shunt617 (R_(d)). However, this method of removing stored energy from thecapacitor 613 is wasteful and accounts for around 50% of the batteryenergy being to be dissipate as heat into the environment. A relativelysmall portion of the stored electrical energy in the capacitor 613 canbe recovered by mounting the shunt resistor 617 to the body of thebattery for heat transfer through the case to the core region. However,a significant portion of the stored electrical energy in the capacitor613 can be used to generate another battery heating cycle after each ofthe above heating cycles using the method and circuit design describedfor the following embodiment of the present invention shown in FIG. 57.

The battery self-heating circuit embodiment of FIG. 57 is identical tothe battery self-heating circuit embodiment of FIG. 55, except for theresistor 617 (R_(d)) having been replaced with the inductor 640 (L). Thebattery self-heating circuit embodiment of FIG. 57 also operates atsignificantly higher efficiency, i.e., with a significantly largerportion of the battery power being used by the self-heating circuit toheat the battery core as described below.

With reference to FIG. 57, the battery self-heating circuit operates aswas described for the embodiment of FIG. 55 up to the point at which thecapacitor 613 (C) is charged essentially to the battery voltage levelV_(B) following closing of the switch 608 (S₁) while the switch 609 (S₂)is closed. In the embodiment of FIG. 57, the stored electrical energy inthe capacitor 613 (C) is then recovered by means of a tank circuit whichis formed by an inductor 640 (L) and the capacitor 613 (C) by closingswitch 609 and opening switch 608.

In the case of an ideal capacitor and inductor, once the switch 609 (S2)is closed, the energy stored in the capacitor 613 (C) oscillates betweenthe said capacitor and inductor, FIG. 57. FIG. 58 (a) shows the plot ofthe current waveform 618 (i₂) flowing through the LC tank circuit andFIG. 58 (b) shows the plot of the inductor voltage waveform 619 (v₂).With reference to FIG. 58 (a), the time location 620 (P) indicates thefully charged state of the capacitor 613 (C), with current i₂=0 and themaximum value of voltage v₂ at point 621 (P) in FIG. 58 (b). The current618 (i₂) increases as the voltage 619 drops from its maximum value at621 (P), FIG. 58 (b). The maximum current point 622 (Q) indicates thatall energy from the capacitor 613 (C) has been transferred to theinductor 640 (L). At this point 622 (Q), the inductor voltage 623 iszero. At this time mark (622 and 623 in FIGS. 58 (a) and (b),respectively), the capacitor energy has been transferred to the inductor640 (L), FIG. 57. Subsequently, the energy in the inductor is pumpedback to the capacitor until the point R (time mark 625 and 624 in FIGS.58 (a) and (b), respectively). However, it should be noted that thevoltage across the capacitor has gone through polarity reversal. At thestart of the cycle, the voltage point 621 (P) is positive and at point624 (R), the polarity is negative. The stored electrical energy has beenreturned to the capacitor by a resonant transfer. This polarity reversalallows the stored electrical energy in the capacitor to be returned tothe battery, for use in the next heating cycle.

Referring to FIG. 58, at the time mark (R), the switch 609 is opened andswitch 608 is closed, FIG. 57, to initiate a second heating cycle asillustrated in FIG. 59. These current 626 and voltage 627 waveformsresemble those in FIG. 56, with the exception that current and voltagepeaks have increased substantially. The point 628 (S) indicates thepolarity reversal of the voltage across the capacitor. The batteryheating cycle of FIG. 56 is then followed by the battery heating cycleof FIG. 59 until the control signal to stop heating is received from thetemperature sensor control circuit 606, FIG. 57.

FIG. 60 illustrates the composite current and voltage waveforms duringboth phases of a full cycle of battery heating, i.e., the initial cycleof heating while the capacitor 613 (C), FIG. 57, is charged and then asthe stored electrical energy in the capacitor is used to heat thebattery core as described above. During the first phase 629 and 630(FIGS. 60 (a) and (b), respectively) the capacitor 613 (C) has noinitial energy and the voltage and current waveforms have lower peakvalues. The energy transfer phase 631 and 632 (FIGS. 60 (a) and (b),respectively) requires accurate timing requests at the points 633 and634 (FIGS. 60 (a) and (b), respectively), and at points 635 and 636(FIGS. 60 (a) and (b), respectively). The second heating resonance phase637 and 638 (FIGS. 60 (a) and (b), respectively) have a higher peakcurrent and voltage. However, all subsequent heating cycles will beidentical.

It is appreciated by those skilled in the art that the switches 608 and609, FIGS. 55 and 57, are electronic, voltage controlled single throwswitches, for example, N-MOSFETs. As a practical matter of increasingheating efficiency, it is important to select components with low seriesresistance, typically less than 1 mW. Lower resistance values areachievable by using multiple switches in a parallel configuration.

It is appreciated by those skilled in the art that the internalresistance and inductance of a battery usually varies with temperatureand even from one battery in a set of identical batteries to another ina batch. For this reason, the self-heating may be provided with amicroprocessor with various battery parameters and the means ofmeasuring the battery parameters as it is connected to a battery andvary the device settings as described above for the embodiments of FIGS.55 and 57 to ensure proper battery self-heating process. As an example,the block diagram of such an addition to the above self-heating methodsand examples of their device embodiments is provided in FIG. 61.

FIG. 61 illustrates the operational flow chart for the self-heatingembodiment of FIG. 57 (it similarly applies to the embodiment of FIG.55). The first step 700 enables self-heating circuit. The enablefunction may be a physical toggle switch or a digital signal applieddirectly to the microcontroller 701. The microcontroller 701 starts theself-heating circuit 702 (the embodiment of FIG. 57 of 55) for a briefmoment, sufficient to capture the previously described voltage andcurrent waveforms driving the battery heating. With reference to FIG. 55(or 57) and FIG. 56, the current 614 and voltage 615 waveforms arecaptured and compared with data held in the microcontroller memory todetermine the battery parameters, such as, the series resistance 603 andinductance 604 of the battery. These together with the capacitor 113,determine the optimal current waveform 114 for efficient self-heating.The capacitor 613 typically comprises of a multiplicity of parallelcapacitors, which when combined add to give the desired capacitor value.In order to accommodate the variation between different batteries, evenif they belong to the same family, for example, Type 31 truck battery,each of the shunting capacitors in the multiplicity of parallelcapacitors is supplied with its own electronic toggle switch which canbe enabled by control signals from the microcontroller 701. With thisswitching capability, the measured battery parameters 703 are used toenable the correct number of capacitors to give the desired netcapacitance value for capacitor 613.

In a similar manner, as described above, the inductor 640, FIG. 57,which is critical to the recovery of the stored energy in the capacitorC, may also require some adjustment. For this reason, the inductor 640may be constructed from a bank of electronically enabled shuntinginductors, which can provide the desired value determined from thevoltage waveform measurements performed. The correct choice of theinductor will provide matching to the critical switching point 624defined in FIG. 58. After these circuit adjustments have been made, theself-heating circuit is ready for operation on demand.

Prior to enabling the self-heating circuit, the remaining batterycapacity may also be measured by a battery capacity sensor 704. Thebattery capacity is measured using established methods based onconductance. If the measured battery capacity 705 is below the presetminimum value, then the circuit ceases operation and issues alert 706.Otherwise, the circuit heating flag 707 is set high enabling normalheating function, which is driven by the output of the temperaturesensor 708, which is processed through the microcontroller 701. Prior toissuing the heating ON signal 609, the microcontroller performs thebattery capacity test. The circuit continues to heat until the measuredtemperature exceeds the set point. The heating OFF signal 710 ceasesheating operation. The above described self-heating circuit maintainsthe battery core temperature at the desired temperature and ceasesfunctioning, either if the battery capacity falls below the set value orthe enable function at the start of the battery heating operation istoggled into the OFF position.

While there has been shown and described what is considered to bepreferred embodiments of the invention, it will, of course, beunderstood that various modifications and changes in form or detailcould readily be made without departing from the spirit of theinvention. It is therefore intended that the invention be not limited tothe exact forms described and illustrated, but should be constructed tocover all modifications that may fall within the scope of the appendedclaims.

What is claimed is:
 1. A heating circuit for generating heat with anenergy storage device having a core with an electrolyte and internalsurface capacitance between the inputs which can store electric fieldenergy between internal electrodes of the energy storage device that arecoupled to the inputs, with one of the internal electrodes coupled toone of the inputs having characteristics of a series coupled resistorand inductor to a voltage source, the heating circuit comprising: atleast one power source couplable to the one input of inputs of theenergy storage device, wherein the at least one power source isconfigured to provide a positive input current and a negative inputcurrent at the one of the inputs when coupled to the one of the inputs,wherein the positive input current flows in to the one of the inputs andthe negative input current flows out of the one of the inputs; and acontroller comprising hardware, the controller being configured tocontrol the at least one power source to provide alternating currentbetween the positive input current and the negative input current at theone of the inputs at a frequency sufficient to effectively short theinternal surface capacitance of the energy storage device to generateheat and raise a temperature of the electrolyte.
 2. The heating circuitof claim 1, wherein the controller is configured to control the at leastone power source to discontinue the alternating positive and negativeinput currents when the temperature of the electrolyte and/or the energystorage device is within an operational temperature range of the energystorage device.
 3. The heating circuit of claim 1, wherein thecontroller is configured to start the at least one power source toprovide the alternating positive and negative input currents at the oneof the inputs when the temperature of the electrolyte and/or the energystorage device is lower than an operational temperature range of theenergy storage device.
 4. The circuit of claim 1, comprising the energystorage device, wherein the at least one power source is coupled to theone input of the energy storage device.
 5. The heating circuit of claim1, comprising a temperature sensor configured to provide a signal to thecontroller, wherein the signal is based on a sensed temperature of theelectrolyte and/or a surface of the energy storage device, and whereinthe controller is configured to start and stop the at least one powersource to provide the alternating positive and negative input currentsat the one of the inputs in response to the signal.
 6. The heatingcircuit of claim 1, comprising a switch, wherein the at least one powersource comprises a component configured to be charged by the energystorage device through the resistor and the inductor of the energystorage device, and the switch, wherein the inductor and the componentare configured to operate as a series resonant circuit with the voltagesource through operation of the switch, and wherein the controller isconfigured to control the switch to start and discontinue heating of theelectrolyte.
 7. The heating circuit of claim 6, wherein the switch is afirst switch, the heating circuit comprising a second switch coupled tothe component, wherein the second switch is configured to initiatedischarging of the component, and wherein the controller is configuredto control the second switch to start and discontinue discharging of thecomponent.
 8. The heating circuit of claim 7, wherein at least one ofthe first and second switches comprises a plurality of transistors, andwherein the plurality of transistors are arranged in a parallelconfiguration with each other.
 9. The heating circuit of claim 7,wherein the controller is configured to control the first switch todiscontinue charging of the component after the component is charged toa potential of the voltage source and is thereafter configured tocontrol the second switch to start discharging of the component.
 10. Theheating circuit of claim 7, wherein the resistor of the energy storagedevice is a first resistor, the heating circuit comprising a secondresistor coupled between the second switch and the component, andwherein the heating circuit is configured such that when the secondswitch is controlled to start discharging of the component, thedischarging occurs through the second resistor.
 11. The heating circuitof claim 10, wherein the second resistor is configured to be positionedin proximity to the energy storage device such that heat generated bythe second resistor during discharging of the component through thesecond resistor heats the energy storage device.
 12. The heating circuitof claim 7, wherein the inductor of the energy storage device is a firstinductor, the heating circuit comprising a second inductor coupledbetween the second switch and the component, and wherein the heatingcircuit is configured such that when the second switch is controlled tostart discharging of the component, the discharge transfers a charge tothe second inductor.
 13. The heating circuit of claim 12, wherein atleast one of the first and second switches comprise a plurality oftransistors, and wherein the plurality of transistors are arranged in aparallel configuration with each other.
 14. The heating circuit of claim12, wherein the controller is configured to close the second switch tocontrol the discharge of the component and is configured to open thesecond switch after the charge from the component has been transferredto the second inductor and the charge from the second inductor has beentransferred back to the component by a resonant transfer.
 15. Theheating circuit of claim 7, wherein the controller is configured toclose the first switch to capture information indicating voltage andcurrent waveforms of the energy storage device, and wherein thecontroller is configured to determine from the captured information atleast one of a resistance of the resistor and an inductance of theinductor.
 16. The heating circuit of claim 15, wherein the controller isconfigured adjust a capacitance of the component based on the determinedat least one of the resistance and the inductance.
 17. The heatingcircuit of claim 15, wherein the inductor of the energy storage deviceis a first inductor, the heating circuit comprising a second inductorcoupled between the second switch and the component, wherein when thesecond switch is coupled to control the discharge of the component withthe discharge transferring a charge to the second inductor, and whereinthe controller is configured to adjust an inductance of the secondinductor based on the determined at least one of the resistance and theinductance of the first inductor.
 18. The heating circuit of claim 1,comprising a capacity sensor configured to provide an indication of acapacity of the energy storage device, wherein the controller isconfigured to enable and disable heating based on the indication of thecapacity.
 19. The heating circuit of claim 18, wherein, when heating isenabled, the controller is configured to start the at least one powersource to provide the alternating positive and negative input currentsat the one of the inputs in response to a predetermined temperature thatis lower than an operational temperature range of the energy storagedevice.
 20. A heating circuit for generating heat with an energy storagedevice having a core with an electrolyte and internal surfacecapacitance between the inputs which can store electric field energybetween internal electrodes of the energy storage device that arecoupled to the inputs, with one of the internal electrodes coupled toone of the inputs having characteristics of a series coupled resistorand inductor to a voltage source, the heating circuit comprising: acontroller configured to: periodically obtain a measurement thatcorrelates to the temperature of the electrolyte, and controlalternating positive and negative input currents provided at the one ofthe inputs at a frequency sufficient to effectively short the internalsurface capacitance of the energy storage device to generate heat andraise a temperature of the electrolyte when the measurement indicatesthat the temperature of the electrolyte is below an operationaltemperature of the energy storage device, wherein the positive inputcurrent flows into the one of the inputs and the negative input currentflows out of the one of the inputs.
 21. The heating circuit of claim 20,wherein the controller is configured discontinue the alternatingpositive and negative input currents when the temperature of theelectrolyte and/or the energy storage device is within the operationaltemperature range of the energy storage device.
 22. The heating circuitof claim 20, wherein the controller is configured to control discharginga chargeable component when the chargeable component is charged to avoltage of the voltage source as a result of the alternating positiveand negative input currents.